UP FROM THE UNDERGROUND recently came Cathy Wilkerson, to cut a deal and cop a plea. She went down in 1970, when the Greenwich Village town house where she and other Weathermen were allegedly making bombs blew up on them (oops!) and they had to flee. She came up still spouting revolution and all that stuff, which was all right until the papers gave her age. It's 35. To talk that way at her age seems unseemly.

Wilkerson was 25 when she went into hiding. She was 25 when the house blew up, killing three of her compatriots, and she was last seen running up the street, running from the smoking rubble of the town house -- half-naked, as the newspapers like to say, although half-dressed would do just as well. And then, after a pit stop at a neighbor's, she was gone, disappeared -- not to be seen for 10 years.

Inexplicably, she reappeared. She contacted the district attorney in New York and she surrendered. She called a press conference in the best Weathermen style and talked about the revolution and Puerto Rican independence and how conditions had not changed and that she had not -- got that, HAD NOT -- changed her views. She was 35 years old and as radical as ever. Even when she copped a plea, she said she wanted to "begin above-ground political work."

This is not as it's supposed to be. You are supposed to get more conservative as you get older. Somehow it would have been more pleasing if Wilkerson had said something about changing her mind, how she had thought it all over and concluded she was wrong. It would have been reassuring if she had come out of hiding clutching back-issues of House Beautiful, saying she was now into taupe and the modular look and that it was time, at 35, to think about children, real estate and Krugerrands.

This, after all, is the pattern. This is what everyone does, and we all have very definite notions about where you should be ideologically for what is called "your age." Ideas and ideologies that are permissible at one age are not at another. Maturity and wisdon, the sort of qualities that corporations cherish in their executives, call for thinking the right thing at the right time -- at the right age. It is not good to be too soon a conservative or too late a liberal. To deviate is to have bad judgment.

We all know this. It is a given and it applies not only to ideas, but to other things as well. A woman, for some reason, is not supposed to wear her hair long when she is past a certain age -- say, 35. Older men are supposed to dress as older men and not doing so does not signal a youthful vigor, but bad taste. The whole thing is almost biblical: To everything there is a season.

The upshot is that we associate aging with wisdom and the two with conservatism. It seems natural to get more conservative as we get older. When it happens the other way, though, or if some radical stays radical, then there is thought to be something terribly amiss. It's as if mother nature has been double-crossed.

Already, Newsweek, noting that the Weathermen took their name form a Bob Dylan song, said that Wilkerson seemed oblivious to the lessons of another Dylan song: "The times they are a-changing." The message is clear: She should have become more conservative and she will be written about from now on as some sort of throwback, a primitive, an ideological wild child who does not know that we no longer care about Vietnam and Puerto Rice and all that stuff. Her own generation will take her measure and, you can rest assured, find her wanting.

But you do not have to be an admirer of Wilkerson or subscribe to her ideas, to see that there is something unfair about all this. She is right when she says that little has changed since 1970 and we should not pride ourselves on how much wiser we have all become, but rather how far we have strayed: how the commitment of every generation to civil rights, civil liberties, the abolition of poverty, the end of all wars (you name it), gets frittered away and lost, misplaced somewhere on the desk along with the bills from Sears.

This is what Wilkerson does not seem to grasp.She is wrong when she says little has changed in 10 years.We have, and we would like it if she would change, too. I mean, she's 35 already. It's time she sold out.