Usually it's when they can start to sit up more and the wind can come up by itself, I think.
That's what happened with DS anyway. I had to spend YEARS (it seemed) burping him after feeding and then once he started to sit up on his own around 5 months and got more mobile generally, I just didn't need to anymore. All I needed to do was sit him down after feeding and he would have a couple of burps by himself. What a relief!!