What are the effects of aging and health?

Health affects the speed of your attacks and the speed of completing dance moves.

In order to slow the aging process you can buy mystical spices and herbs from the Mysterious Traveler in taverns.

The game ends when you divide the plunder at age 50.

The best choice to help prevent this (too late if you've already progressed in the game, but for next time) is to select the "Skill at Medicine" when creating your character. This basically reduces the rate at which you age and lose various speed in skills. The screenshot below may not look like your version depending on platform.

The other thing is to prevent getting captured (by losing swordfights or sieges) because you "rot in a jail cell" which causes you to age, and reduces your health. I use save games effectively to prevent this if my skill isn't high enough.