Hello,
I recently turned 18 and I'm studying with the Open University. I'm going to be studying Computing & IT and Mathematics full time and my degree starts in two days, on the 3rd of October. I've already started studying though, because we get the course materials and websites mid-September. I have really loved what I've studied so far and I would readily recommend the Open University, but with a few caveats.
The OU is the largest university in the country, one of only three to be internationally accredited in the US and well accredited in all of its subjects. It has no entry requirements but getting a good degree classification takes a lot of work, and it's all down to you. You have to motivate yourself to study and keep up with your course, because you're not going to classes or anything like that. There might be local student meetups and there's usually tutorials at local colleges but these are far less frequent than anything at a brick university. If you're okay with that, then you'll do fine.
The Open University is a fantastic opportunity. You might have done really well in school and be able to get into any university you want; or you might be in a position where your grades won't get you far. Regardless, the Open University will accept you for any subject you can think of. A large part of what originally got me looking at the OU was that I could study Computing there without needing a Higher/A level in Mathematics. Funnily enough, this opportunity eventually led to me studying a lot of maths in my own time and deciding to take it as a second subject. My tutors have, when quizzing me about my readiness, accepted that practice as readily as they would a formal qualification. It's not about what you have going in to uni, but the effort you put in while you're there. I admire that attitude.
Additionally, many students nowadays are rightly concerned about the cost of a degree. In England, I'm pretty sure OU course fees are lower than most. In Scotland, it's free like any other form of higher education. I'm not sure about Wales and NI. In any case, you don't have to worry about things like accommodation. You'll be studying at home. As I live in Scotland, my degree is effectively free and faster to complete than normal Scottish degrees (4 years) because it follows the English structure (3 years).
A big caveat and one of the main reasons most young students don't want to study with the OU is that it doesn't have the same culture and socialisation potential. You can meet people through forums, tutorials, local groups, etc. but they'll be of a variety of ages and often have commitments at work or with family. You can't expect things like a crazy freshers week, parties or even being forced to meet new people through classes and dorms. Quite a few courses have mandatory collaborative elements, but some subjects don't have them at all. You could go through your whole degree and barely talk to anyone if you really wanted to. If you're the social butterfly type, it's unlikely to appeal to you. For me, it's perfect because it's a calm, serious environment for study, and you know that everyone is there because they want to learn.
So it really comes down to that core question: are you going to university to learn or to have fun? If your focus is learning then the OU is just as good as anywhere else, possibly even better, but you'll have to make your own fun.
Good luck.