There PvP after lvl 28?

Where and how to PvP after lvl 28, and then I was lvl 44 pvp lvl only 26 and I want to but now that I'm lvl 44 I can `t click Join PvP in the second act is the problem help? Maybe it depends on the league in which I play?

your pretty much screwed for pvp until you get to at least lvl 70, there isnt any more pvp past lvl 28 until merciless act 2, and once you get there dont expect to pvp that much because it is dead in standard right now, only a few active pvpers and those guys are geared to the teeth so it wont be a fair fight even if you get to 70. sadly, until GGG does some updates specifically for pvp i dont see it recovering any time soon.