That's only true for most of the preexisting players, most regens will be at their best by the time they're 25-26 if they get played often. By the time they hit 30 their physical stats do tend to start to drop, some last until 32 or so but not many and at which point you've usually replaced them with someone younger.
Interesting point but i'm not sure why it would be different for regens. What i've read before and experienced is the reason regens might seem to peak earlier is you tend to play them more from a young age (especially if their highly rated) and they then appear to hit their peak in their mid twenties then start to decline at 30. But by overplaying when they are young the PA they hit at 25 is not as high as if they had developed slower and peaked nearer 30. It might only be half a star or 20 PA points or so but it makes a difference. As I said earlier this what i've found and read from others but you might have different experience.
If you think about this is what happens IRL. Players like Owen overplayed when a teenager, was at his peak in early 20's then burnt out by 30. Where as players like Giggs, Scholes and Beckham were managed properly and were at their best in late 20's and Giggs and Scholes still playing at top level at nearly 40. Think how good Owen could have been if had been at United as a teenager rather than when he was already past it at 30.