There's no limit, Rich. My wife just finished a graduate degree she had to get to keep her teaching job, due to a change in accreditation requirements at her school...she is in her mid-50s.
My wife at the time got her masters in Sp/ed in her early 30's. With her new degree and job her salary almost doubled.
Rich as somewhat already posted, the regrets over things not done are harder to live with than the regret over things done.
I went back to school in my 40's. I was scared about having to compete with people half my age and the fact I hadn't been to school in 2 decades.
One afternoon myself and a couple other of the older students were outside smoking and shooting the breeze while on break from a class. the Instructor joined us and we asked how were doing, he said we were all doing fine in fact were tops in the class. we asked how that could be when the youngsters should still have some of the information still fresh in their minds and more disciplined study habits. he said us older students because of life experiences were better at picking out the salient matter from the chafe and applying it correctly.
I CLEP'ed all allowable courses and made the deans list both Semesters attended. I felt pretty good about that. Shortly thereafter my boss (me) and my tax accountant said I warranted a raise.
Needless to say this was not a liberal arts degree program.