I hope they last evenly.
I have seen examples of both extremes -
I knew a lady who was very health conscious all her life - proper diet, lots of exercise, and such. As she neared 100, her mind "died" (she was gone) but her body was so healthy that it kept going ... and going ... and going. Her body finally joined her mind many months later (her son was at her side every day).
I knew a man who was a professor. Extremely intelligent. He knew several different languages, taught English to Japanese students, excessively book learned (had a massive library). Yet just after he retired his mind went (dementia). It got so bad that he even forgot how to go to the bathroom. He finally died of neglect in a local nursing home on a christmas eve (all alone).
I hope agility of mind lasts longer. I can have quality of life with an uncooperative body, but there is no quality of life with a mind that doesn't work.