When I think of aging, I think of
1) gray hair and trying to keep those hairs colored
2) prescription drugs and their side effects
3) stress from the job, teenage children and aging parents.
Anything else, you can think of?
Well, I have clientele from ages 14 to age 84. I myself will be age 43 this year. I can tell you that all the crazy chemicals and colors that you experiment with at a young age can be done at any age, but if something goes wrong, your "recovery" is a little longer as you get older.
Also, many people are forced into double processing (permanent color and relaxers or permanent color and curly perms) due to graying. Two chemicals compromises the integrity of the hair at any age.
I personally think that our scalp recovers from decades of abuse, but I will also say by the time you reach age 40, full recovery from relaxer burns and haircolor irritation may not happen.
If you are interested, you can research about DHT hormones and genetic balding which is a totally different discussion.
As far as retired individuals are concerned, I suggest discontinuing as many chemicals as you can if you do not have a corporate job to impress.
I also suggest that if your corporate job is stable and your manager is in agreement, "micro-locks" and "natural hair" should be considered as you approach age 40 or whatever age where you find that you are taking more prescription drugs. For some people, that age is younger than age 40 and for others - well past age 40.
In addition, if you notice too much thinning, and you are age 24 - that is a clue that you are doing too much to your hair.
At the end of the day, your age is "nothing but a number." If you have a drug-free lifestyle and try to stick to healthy lifestyle choices most of the time, then you can be age 50 and double processed and still recover quickly from some lazy hair days and too much curling iron usage for a week. I have seen it.
Your hair will stay as youthful as your body feeds it unless family history of genetics are beyond your control.