Id personally say it is what you make of it.
Im 23 studying a 2 year part time foundation history degree at oxford, with a view to either going into the 2nd year of a history degree full time or starting in 1st year studying law here. (still undecided on that but both are fascinating in different respects)
Im one of the youngest on this course and to be fair it dosent bother me, so i would expect that would be transferable in a polar situation.
I have made plenty of friends here, from first year students, up to 3rd years, postgrads and tutors, aswell as the slightly older people on my course. University is what you make of it and what you want to get out of it that counts in my eyes.
As LewisH has said you will find having some more life experience and worldly tales, you will study slightly differently. My aim is to take things more seriously from the get go, not only does it look good to tutors (and there more likely to help you out in a jam if you keen), but the grades and marks gained in 1st year are very much a banker in the sense that most 1st years go out most nights and coast through with a 50 or 60 when in reality the ever desired magical 70 is highly and easily achievable, and i expect most mature students will hit this, or at least get very close to it.
Also if considering applying to oxbridge or the other historic universities, dont be too upset about what college you get put into, as they generally have a dedicated college for mature students, i know here we have Manchester Harris, not sure about cambridge and durham however. It is essential to remember that these colleges are assigned (if applying openly and are not too bothered) for you and to where they feel you would most comfortably fit in, and it is a decission the faculty and colleges make together. The awarding body on your degree certificate will say whatever university it is from, and does not mention colleges, to my knowledge at least.
Dont stress too much about being classed as different, if its something you feel ready for and truly want to do, go for it, they will be the best years of your life, that is certain. 1st years and other people on the course wont care about age, they will care about you and what your like, so inevitably you will clash with some personalities, thats life.
Good luck with you application, if you want any help or advice feel free to pop me a message.