I am at the end of my second year of physio now (aged 33). For me, I had done a degree previously, and as I had a 2:1 from that could apply straight to the course. If you don't meet the entrance requirements, you might have to either do A level sciences, or as is more likely, a year long access to healthcare course. The best way to ascertain what the entrance requirements are is to e-mail the universities you are interested in directly and ask. Within my year of 60 ish students, I would say that around half are mature (over 21), so there are definitely a lot of us older lot going to uni - you won't be alone!
The same loans and grants are available to mature students as first timers. For me, I get a NHS bursary and a student loan (cut rate because of bursary), and this alongside working long hours keeps me afloat - I am in the fitness industry too, personal training and class instructing, so similar background. I've not found it hard being older at all, and actually with a full on course such as this, I have found it a benefit as I don't want to go out and get pissed every night at the student union. That is against the fact that I have to work 15-20 hours a week ontop of uni, which is certainly a challenge, especially when I am doing my 5 week placement blocks and am in hospital 9-5 Monday to Friday.
I would say your first step is to work out where you want to go. Then mail the unis asking what they want. Then you will have an idea about how you can get into those institutions and take it from there. It is very very much doable at any age, you just have to want to do it. Oh yeah, as you have an inside link with hospital, I would go about arranging work experience with the physio departments - this is something that is pretty much a must have for any interviews that you get.