I count Ava Devine and Lesley Zen as looking way too young to be considered mature. For me, under 30 or those who look like they could be under 30 are average. under 23 is very very young for me, and while it is hot, I still see them as teens, in a way, unless they look older.
Older women I adore
1. Donita Dunes
2. Fnacesca Le
3. Ashlyn Gere
4. Houston
5. Blake Mitchell
Tiffany Towers, Vicky Vette, Lisa Lipps, all are fantastic. Alexandra Quinn, and all those girls who came back from the 80s/early 90s looking better than ever: Ashlyn Gere HELL YES... and what's her name... goddess... FRANCESCA LE. HELL YES. The only ones I never got into were Tyfanny Million and Jeanna Fine, and I've never been a big fan of the older Juli Ashton, Sunset Thomas, Marilyn Chambers...
That's all I can think of off the top of my head.