"Aasimar mature at the same rate as humans, but they can live up to 160 years."

Agreeing with Oofta, they would age at the same rate as humans until they reach maturity, but when you consider them mature, and what happens then are up to the DM.

You might decide that someone is mature when they go through puberty, when they have reached their full height (18 to 20) or when the brain generally reaches full development (25). You might decide on some other benchmark.

From there, they could continue to age at the same rate as humans, but just continue to live for 60 to 80 years longer in a diminishing state (with giant ears and noses), or they could age at ~ 40% the rate a human does. The rules do not specify the rate, or condition, only the lifespan. I believe most DMs would go with the ~40% of the human aging solution, though.

Elves, in my campaign world, age at the same rate as humans until age 30, and then they get stuck there. As they approach the end of their natural life span, the aging process resumes and they age at the same rate as a human over the next 30 to 70 years (until passing). Their aging process resumes when they are ready to pass on, meaning that elves can technically life forever if they never find themselves ready to go. Dwarves, however, age to about 30 at the same rate as humans, and then their aging slows dramatically. The more fire and passion in their life, the slower they age. A dwarf that is lazy and bored might pass before their 100th birthday, but a dwarven master craftsman that loves his craft and works every day might live 600 years. Dragonborn, meanwhile, age very quickly to adulthood and then stay at that age - forever, physically. However, they find themselves becoming more passionate and reckless as they age, which inevitably gets them killed at some point. Kobolds, however, do not know their natural lifespan because those suckers always end up under someone's boot.

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