This is the kind of example I'm talking about
This guy is what? Maybe early 60's? Think if he had gotten a transplant at 25 what his head would look like now. This is the exact reason why hair transplant should be thought through better at a young age. That said....a person should be able to reasonably tell even when they are young if they can get it done. If a person has had thin hair all their lives its probably best to wait. It they had crazy thick hair chances are they will not look like the guy in that picture in the future and could probably take a chance on a hair transplant a bit earlier.
I fall into a middle category. Never had super thick hair or thin hair. If I get a hair transplant now I should have decent coverage until old age but nothing spectacular...
I disagree with you.
It is not as simple as you suggest to determine whether a hair-transplant will be prudent at a young age, simply based on how thick your donor hair is at that time.
Androgenetic Alopecia is a progressive condition with an often hard to predict progression and timeline.
And contrary to what the Norwood-Hamilton scale suggests, the majority of men who start losing their hair at a relatively young age, will eventually experience thinning and recession in the occipital region and the nape (in other words the donor hair).
I think those best suited for a hair transplant are unfortunately late-life balders. Ironically they are the men who deserve it the least, because they had a full head of hair in their youth.
For early-balders, a hair transplant can still be very successful, if you are lucky in having robust donor hair, or if you find a surgeon who can utilise beard, armpit, pubic, and even leg hair.
In fact I think the use of non-scalp hair for a hair transplant is perhaps the single most important resource all balding men have.
This non-scalp hair is much more robust than scalp donor hair is, it is not sensitive to DHT, it is unlikely to atrophy or even grey like scalp hair will, and we have abundant supply of such hair on areas on our body that will not miss it if it goes.