Do you mean had a successful career in a non-tech field and making the switch?
My running theory is that companies know what they're getting into with a bootcamp grad, and what is important to them is that the candidate is a quick learner, hard working, and motivated. Someone unproven like a college dropout, or someone who has worked retail for the past few years will have a much harder time proving that.
I think a 31 year old would fit in just fine.
I can't comment on App Academy because I have not taken their course.