In preceding columns in this series we have talked mostly about the financial aspects of retirement planning. Important? Sure. When you retire there will be major changes in your financial situation -- and you had better be prepared for those changes.

But perhaps equally important will be the changes in your lifestyle. The most significant of these will be your allocation of time -- those 24 hours in each day that don't change after you retire.

In the first place, you should have more than one interest. Even if it's an activity for which you have an abiding passion, you simply can't address yourself to a single project for any long period. Several activities are preferable, and they should have different characteristics: active vs. sedentary, physical vs. mental, group vs. solo, etc.

Whatever you select should be something you really enjoy. Just filling up time slots won't satisfy you for very long. With most leisure-time activities, there is usually considerable enjoyment, even excitement, in the anticipation and planning -- but only if the activity itself is pleasurable.

It's highly unlikely that you will be able suddenly to turn on an interest the day after retirement, or that a previously unthought-of-interest will suddenly be able to turn you on. Start now to think about the many things you might like to do; and if at all feasible, sample some of your ideas.

Test runs should permit you to weed-out those that definitely do not appeal to you. When you find something you enjoy, pursue it now, at least on a small scale. In addition to being better prepared for retirement, you may even find it contributes some unexpected spice to your life now -- a serendipitous complement to your working hours.

Please don't get the idea that I'm suggesting that at 45 you're over the hill, that your career has run its course, and that it's now time to switch your declining energies to other, less demanding fields.

On the contrary, the late 40s and 50s and into the 60s should be your most productive years -- the period when you can apply the accumulated experience of the first 20 or 25 years of work.

What I am suggesting is that by the time you're 45 years old you should have accepted the inevitability of aging. If you face up to the probability of eventual retirement, then you should recognize that advance planning is the best assurance of a successful transition.

Having a house by the side of the road to watch the world go by may work out for a few people. But for most -- particularly if you've had an active and stimulating working life -- stagnation can be a terrible affliction.

It doesn't matter whether you collect something old or create something new; go back to school to learn -- or to teach; read about exotic places, or travel to them; try gastronomic dining, or cooking -- or both; go back-packing on the Appachian Trail; or bird-watching at your local park.

What does matter is that you find something you enjoy and can get enthused over. There are books and magazines on just about any subject you can think of (and a lot you can't), as well as special-interest clubs devoted to an amazing variety of activities.

In short, broaden your horizons -- and do it now! Planning for and developing a variety of interests is just as important for a satisfying retirement as your financial preparation.

There's a whole new world out there waiting for you; but there is no free lunch. You have to enter that world on your own -- and don't wait until retirement day to take the first step.