@minkimania aww :( i've found that it honestly really depends on the rat. the first time i had rats, they didn't let me touch them until months later. this latest time, they warmed up in like a week which was insane (but they're just very crazy in general). sounds cliche, but my advice would be to give him time and don't get discouraged. also, i've found that going to pet them can be really scary for them at first, since it's literally just a giant hand advancing toward their face. they usually have to get used to your scent, as weird as that sounds. let him just sniff you at first. you can place a treat on your wrist or somewhere on your hand where he'll have to step onto you in order to get it. really, just take it slow. that's the best i can give :/ good luck!
(also thought i'd point out, i've only ever had female rats.)