Wear whatever makes you the most comfortable.
most dudes still wear tighty-whities so actually you dont have to wear boxers it just that most prefer boxers over tighty-whities because thats what most young children wear...thats how i feel but i think briefs and tighty whities is almost similer it jst a mix of boxers and tighy whities
When you feel more comfortable in boxers, I suppose.
Start right now
Whenver you feel like it's time to change. I still wear Tighty whities. I have boxers and boxer briefs too but I mostly wear Tighty whities.