"Your brain will undergo an change around the age of 25"
Yes, but exactly the opposite. You will get 10 times more miserable, because the depression will kick your ass in order to give it all you got in a last-ditch, desperate effort to find a mate and procreate.
Copes (masturbation/porn and video-games) stop working. You'll get tears trying to watch amateur videos that are younger than you having the time of their lives. Even playing the latest and greatest video-games you can't concentrate on it, because you will think all the time your miserable situation and what more you could do to get a girlfriend.
"You will feel less anxiety about achievement"
If you have not achieved anything in life, then you will get more anxiety, not less.
This is my own experience.