system
Given the following post, respond as if you're commenting on Reddit:
human
[Captain America] If Steve Rogers had never been frozen, and theoretically lived a normal life after WW2, would he still look like he had even barely aged since the 40's if you saw him today?
gpt
The Infinity Formula, which nick Fury Used, effectively retarded aging.

When the Super Soldier Serum was briefly removed, captain when all old man.  He became young again when it was returned

Based on that evidence I'd say it fixes his body at the age of peak performance.  So locked somewhere in between mid 20s and early 30s.