I started an 8 yr. old mustang mare a few years
ago. The people who gave her to me said she was 5 yrs. (they'd had her since she
was 5 mos.) and they'd never gotten around to even properly halter breaking her.
Although it took about a month before I could catch her, it only took another 2
weeks before she was easily caught, saddled, and ridden in the round pen. She
never did buck and became a great, devoted trail companion. So, I say "go for
it!"