The ups and downs of life may seem to have no predictable plan. But scientists know there are very definite patterns that almost all people share. Even if you've passed some of your "prime", you still have other prime years to experience in the future. Certain important primes seem to peak later in life.

When are you smartest? From 18-25, according to I.Q. scores; but you're wiser and more experienced with increasing age.

You're sharpest in your 20's; around 30, memory begins to decline, particularly your ability to perform mathematical computations. But your I.Q. for other tasks climbs. Your vocabulary at age 45, for example, is three times as great as when you graduated from college. At 60, your brain possesses almost four times as much information as it did at age 21.

This trade-off between sharpness and wisdom has led psychologists to suggest that "maturity quotients"(M.Q.) be adopted for adults.

When are you happiest? You have the best physical sense of yourself from 15 to 24; the best professional sense from 40 to 49.

Before age 24, we believe that our happiest years are yet to come; over 30,we believe that they're behind us. A National Health Survey agrees: After age 30, we "become more realistic and do not view happiness as a goal in itself. If we maintain our health, achieve professional and emotional goals, then happiness, we feel, will follow".

When are you most creative? Generally between 30 and 39, but the peak varies with different professions.

Mozart wrote a symphony and four sonatas by age eight, and Mendelssohn composed his best known work A Midsummer Night's Dream, at 17, but most of the great music was written by men between 33 and 39.

Though the peak in most fields comes early-most Nobel prizewinners did their top research in their late 20's and 30's-creative people continue to produce quality work throughout their lives. For the "well-conditioned mind", there is no upper limit.