Even in Philly, the top attractive performers are in the 35 - 50ish range (some even older). Mind you, they are still very attractive and better yet, they really know how to treat a man. These places have better service than the spas out in the burbs at the same price. You can find some lesser popular spas with younger girls, that may even have lineups to choose from, but you will not get the same performance. Maybe the only benefit is that they are a little cheaper.
At the more upscale agencies in Philly there are model quality younger girls (although even at these places their real age could surprise you) and they come at a premium price for premium service.