Do you mean experience of an OU student loan or experience of an OU degree at a 'mature' age? If it's the latter, then I do have experience. I started my degree at age 45 and finished at just gone 50. It was in Social Sciences, which included sociology, criminology, social policy, human geography and culture, media and identities, plus the first foundation year. I absolutely loved every minute of it! I had two school age children at the time, but they were secondary age so didn't need constant supervision. I used to spend about 2 - 3 hours a day on it, varying depending on whether an assignment was due. I even took my books on holiday and was often seen on the beach with a book and a highlighter pen!
I can't help with the loan aspect - sorry, as such things didn't exist in those days. It cost me about £350 a year - I guess it's a lot more now. It was great though and, given the funding, I'd undertake a Masters now - not for any other reason than I loved it!
Good luck and let me know if there's anything else you need to know, but I bet there are quite a few others on here who also know what it's like. x