system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do men get hairier as they age?

My understanding is that testosterone  peaks at a relatively young age (20s) but many men don't grow a lot of hair on their face or body (or weird places like nose and ears) until they're older.
Why is this?
gpt
The top answer isnt quite right.
Testosterone is primarily an anabolic hormone - meaning it helps you to grow muscle.
It can be converted into DHT, which is an androgenic hormone - meaning it causes things like hair growth.
5-alpha reductase, which is an enzyme, does the conversion.

Hairy people have more DHT not more testosterone.
As men age, we produce more 5- alpha reductase, which converts more of our testosterone into dht making us hairier. The reduction in testosterone level by conversion makes it more difficult to build muscle too.

Incidentally, DHT also regulates the prostate, and too much can cause unhealthy enlargement.

Tl;dr hairiness caused by dht not testosterone. With age we produce more of an enzyme that converts testosterone to dht.