I don't believe age has anything to do with your mother's hair losing its thickness or health. Oprah, who is 50, is a good example. In fact, there was a black woman on Oprah today (speaking from the audience) with very pretty, thick grey hair. I've seen many black women with very long, thick beautiful grey hair.
There are also many on this board (from previous posts) who are very young with grey hair.
Your mother may need to check her diet and make sure she is getting all of her vitamins and minerals, like B vitamins, copper and zinc. Medication can play a role in the thinning of hair, at any age.