VDP is better than ever at 30.He needs to win PR and MSR in the next 2 years. If not, I don't believe he will do it anymore.
Pedersen is stronger than ever at 30.
Roglic is finding it increasingly difficult to perform all year, but he's a favorite for the Giro at 36.
Gilbert won Roubaix at 36.
We don't know when Pogacar's decline will begin.
It's normal to slow down performance first in long-duration races like the GTs. He might continue trying the classics for 2-3 years when he can't compete in the Tour.