I did my first degree from 1997-2001. Graduated with a 2:1 in English/Computer Science and then went to work in the city. Spent 6 years in various roles from programmer to more managerial/project management stuff, and hated pretty much all of it. Voluntary redundancy came up and I thought why not. Spent a couple of years getting qualified in personal training, athletics coaching etc, and then started to get interested in how the body works from people I met with injuries. Thought about doing a sports massage course, but then thought well why not go the whole hog and apply for physiotherapy.
So, sent off my UCAS January of last year a couple of weeks before the deadline, and here I am approaching the end of my first year of three studying physio.
To answer your questions about mature students and funding. I am not eligible for a student loan as I have already had one before. This is applicable to all but a few circumstances I believe. I think you can get a second student loan for medicine from memory as an example. As he has never been to uni, this wouldn't be an issue though. He would also be entitled to whatever additional funding an 18 year old would get. I have also got additional help from the university as I am on a very low income (as are most students hey...).
My advice to him would be to do it. I'm going to be 34 when I graduate, but thinking about it, you still have 30 plus years of your working life ahead of you at that point. If he isn't liking what he is doing, then change it. Thinking about leaving a well paid job for student days again is scary, but its incredible how resourceful you can be when you are forced. I am doing coaching, spin classes and sports massage on the side, and along with my grant am just about surviving. Ontop of this, I am so much happier now than when I was earning £35k a year but hating every single day of work. I don't think you have to get into loads of debt to go through uni - I'm not so far, and haven't needed any help off the bank.