How soon is it ok for couple to try dry humping?

So my boyfriend and I have been dating for almost 3 months, and up til now we've only been making out. He's mentioned trying dry humping a few times because we both want to do more physically but we are unwilling to do anything that constitutes sex (clothes must remain completely on). I was just wondering about how far along into the relatonship most people get before trying this out. (I just grauated high school, btw)