insulin is closely related to aging aswell.
therefore 1. overeating and 2. insulin abuse contribute to a huge part.
steroid users dont necessarily look much older, however add in slin (which mostly happens in conjunction with GH) and you get some 40-looking 20 year olds.
i think GH alone actually has anti-aging properties, slin does the opposite.
strong androgens create a masculinized look, this may contribute to looking older.