No. There's no reason you can't do this. It's just that most age builders are still learning techniques and don't spend the time to give the age the depth to really make it shine as well as others. But all the things necessary to give the textures depth and randomness are there. There's a few tutorials on the wiki that cover things like blending of materials and decals etc. I'd suggest checking them out if you're interested in giving more depth and life to your age.
Texturing Just scroll down to texturing and check out what's there. There's a few things not covered. Giving objects like books and pedestals shadows etc. But it's all fairly simple and straight forward. Good luck