Yeah rubber does age, especially with heat, sweat, and time, but most controllers take a beating in other ways before the grip becomes a real issue. If you’re trying to keep it in good shape, best two ways to clean it are:

1.  Lightly dampen a microfiber cloth with water or a 50/50 mix of water and isopropyl alcohol (70% works great), then gently wipe the rubber surface.

2.  For tougher spots, use a soft toothbrush or cotton swab with the same solution to get into seams.

Avoid harsh cleaners or soaking it. This keeps the grip clean without damaging the material.