I'm 32 and am going back to school full time in the fall to get my MS. Do I wish I had done this many years ago? Yes. Do I wish I had done it straight out of university? No. While getting my BS, even with a lot of co-op experience (my school alternated 3 months classroom then 3 months work through all of university) I didn't fully appreciate how important certain concepts I was learning would be and how useful a lot of the things I was being taught would be. Over the course of my first few years of working, so many things that were just abstract concepts during my undergrad education really 'clicked' and I came to not only understand the concepts a lot better (when to use a certain formula and why), but also how to tie together subjects that were completely separate in university. If I had gone straight into a MS without working I'm not sure I'd have gotten as much out of it without the practical experience I gained in the first few years of working as I'm hoping to get out of it now. My big worry about going back after working for a while is remembering calculus. I've been going through all my undergrad calc notes relearning it all, and I'm shocked at how much I've forgotten (laplace transform? yeah, um, can't the intern right a matlab program to solve this for me?). I'm confident I'll be ready in September, but spending my summer teaching myself multi-variate calculus again doesn't sound very exciting. A lot of the other subjects, like mechanics of solids, thermodynamics, etc I have used often enough to be able to retain a lot of what I learned. If I were getting a MS in Engineering, the 'engineering' subjects would not be a concern, just the math behind them.
As to why I'm going full time instead of part time? My situation is kind of unique. The program I'm taking (MS in Radiological Physics) is only offered at a handful of univeristies in North America, one of which happens to be in Detroit, about a 20 minute drive for me (40 minutes if the border is backed up). Because I'm Canadian and still living in Canada (commute to work in the US every day) I can't legally work and go to school in the US at the same time, as that would require two visas and the Border Guard I talked to about this said I can't have two visa's at once. So I'm forced to either quit my job and go full time, keep my job and take a different program part time at the University of Windsor, or move to another city in Canada where it's offered and try to find a job and go part time. Also, I just want to get it finished, so going full time would have been my choice regardless of Visa issues.
Bob