If you really want to do it, go for it. I trained with someone who was 40 when they graduated - came from a background of media PR or something, didn't have a science degree - and he was a fantastic doctor.
George's is the best place to be, tbh - but then that's where I went so I would say that. They have been the mature student specialists for years, way before they introduced the GEP - I think it was 10% in my year.
The GEP course is 4 years, but they'll still take graduates on the full 5-year course - talk to the admissions tutor and see if you can go in for a chat. The faculty are very approachable and keen to get loads of different types of people onto the course.
Cons - bloody hard work, especially the GEP, and you do have to do evenings/weekends to get the most out of it and give yourself the best chance of passing finals. In the latter years, it really is more of a job - 9-5 or 8-6 Monday to Friday, and you're in seminars/lectures/labs when you're not in clinic/theatre/the wards.
Wrt careers, you have to realise that some avenues are going to be less accessible than others. What did you want to do?