we have seen active officers in excess of 130 on the show. Starfleet hasn't had a mandatory retirement age since at least 2270. McCoy was only semi retired when he toured the Enterprise-D in 2364, at the age of 137.
Retirement is a concept we have now becuase our bodies break down and can no longer function they way they did in the past. We also like the idea of being able to just relax and not have to work. So, I think in the world of Star Trek. They don't even see everything as work. And considering how good their genetics and health are. Retirement is probably something seen at the end of a very long career or something that is done when you fall into a condition where medicine can't help you. Though I wonder since money is really a concept it really changes everything. I would think people would stay at home and raise their kids. There wouldn't be as much of a rush on life.