THERE ARE two questions you must never ask and never answer, Miss Manners' grandmother used to say:

1. "How old are you?"

2. "How much money do you have (or make)?"

Miss Manners' grandmother was not, as you can imagine, the sort of lady who fooled around. Another of her maxims was "Colored stones are vulgar," and so she gave away any family jewelry with rubies or sapphires, thus saving Miss Manners herself from the temptation of eventually falling into such vulgarity. All her descendants naturally bless her for this. The family was never rich, but we try to behave ourselves.

With such sensitivity, it is fortunate that Grandmother Manners did not live to hear of a whole world of other unanswerable questions that modern ladies are asked. But Miss Manners trusts that she will not be dishonoring the dear lady's memory by suggesting that it is, perhaps, time to halve the original list.

It is as vulgar as ever to inquire into, or confess to, the state of personal finances. We do not judge people by the amount of money they have (do we?) and, therefore, any interest in such amounts is unseemly.

But why should age be considered unmentionable?

As a matter of fact, it isn't always, and never has been. One could always ask people under 21 what their ages were ("How did you know they were under 21?" you may well ask), or men if they were successful and under the age of 40. The tabu really only applied to grown-up women and to both sexes between the ages of 40 and 75, when it became all right again.

In examining this pattern, Miss Manners detects an unpleasant suggestion that while being very young or very old is considered rather fetching, being fully grown-up is not, particularly for women. Our most usual form of flattery is to tell people that they look much younger than they are, such compliments often being supported in the most ludicrous fashion.

This attitude keeps everyone in a state of petty falsehood and perpetual dissatisfaction. How discouraging to live in a society where the natural progress of life is considered to be a downhill movement.

For her won experience, Miss Manners has found age to be less of a distinction than character in determining the worth of individuals, and finds that her inner circle of friends range in age from 8 to 85.

She can nevertheless see that age does bring change, but its chief movement seems to be in the direction of sense.

She is therefore rebelling against Grandmamma's dictum and, when asked, discloses her age. (She does not ask others for theirs, however, in case they do not care to follow her lead.)

But she promises, faithfully, not to run around dripping with rubies and sapphires. MISS MANNERS RESPONDS

Q. My sister and I are close. Our husbands have become friends during the past 20 years. Now my sister and her husband are experiencing a long and unhappy, but not yet legal, separation. Although my brother-in-law has lived with his girlfriend throughout the separation, he and my sister still profess a desire for reconciliation. How do my husband and I conduct ourselves without offending my husband's right to friendship, my sister's wounded feelings and my loyalty?

A. If your sister and your brother-in-law make their separation legal, you and your husband may certainly entertain them separately with whatever partners.

There are too many such disruptions now for anyone to expect others to participate in their separations. If however, you pursue this fair-minded policy during the trial period and there is a successful reconciliation, they could easily, in their new harmony, transfer residual feelings of ill will to you. Worse, you could get stuck with the friendship of the now deserted girl friend. It seems to Miss Manners that a temporary policy of blood over friendship would be practical.

Q. I play in a weekly poker game with several of my neighbors and we are faced with a dilemma.One of the newer players has become a nuisance. He has a tendency to cheat on the amount he puts into the pot and feigns naivete when caught. It has gotten to the point where we must watch him constantly to insure that he does not shortchange the kitty, and this has turned a formerly enjoyable pastime into an ordeal.

One week, we decided to move the game without telling him. He drove around the neighborhood until he found the spot where all our cars were parked, and had the nerve to come in and play. He is insensitive to any such insult or "subtle" hint that we would rather not share his company, but not one of us has the guts to confront him to say we are throwing him out of the game. We have never been faced with such a situation before. What is the correct way to bar this unwanted player from future games?

A. In a time of changinc moral values, when sympathy is expected to be the proper response to unsocial behavior, cheating at cards is about the only clear-cut, unforgivable crime left.It is nice that you are trying to be subtle, but your hints are, as you have noticed, too subtle. Tell him, "We are sorry, but you are no longer in the game." This is sufficiently subtle, if you compare it with the traditional American method of dealing with people who cheat at cards.

Q. Could you give me some taste guidelines about designer clothes? I an now in a position to upgrade my wardrobe, having taken a new job with a much improved salary, and am at an age (28) where I feel I should dress nicely. The clothes I can now afford, and which I like best, are the "designer boutique" sort, frequently bearing the initals, insignia or the name of the designer. I understand you object to this, but I don't quite understand why. I am not above letting people know that I care to dress will. Is there anything wrong with a good designer putting his signature on work he is proud of? Please tell me why you consider this in bad taste, if you do, and whether I am likely to be embarrassed in wearing such things before others who may feel as you do.

A. The worst instance of embarrassment in connection with such clothing was suffered by Miss Manners herself, who found out that a lady of her slight acquaintance whom she had been addressing for years as "Mrs. Klein" wasn't a Mrs. Klein at all. How was Miss Manners to know? By every indication, the woman's name seemed to be Anne Klein and that of her husband, whose T-shirts she apparently often wore, to be Calvin Klein. Miss Manners, indeed, thought that the family names were emblazoned somewhat exaggeratedly on their clothes, but assumed they had had bad experiences as children, when their mothers forgot to sew name tags on their clothes for summer camp.

It turned out that the Kleins were unrelated artisans whom this woman was helping to advertise by allowing space on her body to call attention to their work. Miss Manners does believe in encouraging good craftsmanship, but finds this method excessive. She, herself, and most people who appreciate good dressmaking and tailoring, can recognize quality without having to read the label on someone's sleeve or bosom or worse.

Q. The other night, my family and I were having a discussion. My father said that nowadays it was acceptable to pick up lamb chop bones with your fingers to get the last few bites of meat, in a restaurant. We all disagreed with him and made a bet. Please answer this soon, and settle the bet. I could use the money.

A. It is yours. But when you take it, please express Miss Manners' warm sympathy to your father, whose principle of not wasting food Miss Manners finds throughly understandable. In fact, Miss Manners began her career, among Victorian families who thought is a status symbol to waste food, as the heroine of the admonishment, "Leave something on your plate for Miss Manners." We no longer believe in this arrogant behavior, and Miss Manners has found more dignified sources of nourishment. She does not like to see good food wasted; however, she cannot carry it so far as to recommend gnawing at lamb chop bones in public. Tell your father that much can be accomplished in the way of digging, with a sharp and agile knife.