Most of the student body (I believe the ratio is about 2/3) at Oxford are undergrads, aged 18-21. Most colleges cater to these students. They are largely of English descent and ridiculously smart in the same way (they call them "bright young thing" here). Graduate students are more internationally diverse and smart in different and specialized ways. They generally matriculate at age 22-25, with notable exceptions. Thus, at 30, I am one of the oldest graduate students.
With age comes certain things: wrinkles, experience, less anxiety about all sorts of things, and resources that allow one to surpass just-above average subsistence living characteristic of student life.
That said, there are few things I have had to become accustomed to while here, some of which I wished I had known beforehand, about being a mature student which I share here.
1. Institutional Support
* University-wide - There is a "Mature Student" organization, but it is largely for undergrads over 21 (I found this humorous).
* College-based - The college is designed to be supportive. The best support can be acquired through a strong MCR (which, again, stands for "Middle Common Room" as opposed to the junior (undergrad) and senior (fellows, or college faculty) and represents both a place and the student body). I would advise graduate students to go to a college which has a strong, cohesive MCR. LMH (Lady Margaret Hall, my college), has one. Look for in-college graduate student accommodation. Several of my classmates are in great, name-brand colleges (St. Catherine's, Magdalen), who have a very weak MCR and are very unhappy with their social life and feel completely disconnected to their college. There are also several all-graduate colleges, such as St. Anthony's and St. Cross.
2. Being Married
* Housing - So far as I know, St. Anthony's is the only college which has in-college accommodation for couples or families. A few have couples accommodation outside college or through generic University housing (I've heard these are awful, sometimes far away, but subsidized). That simply comes with the nature of the beast - Oxford was founded as a monastic-like seminary for single and separate clergy. Nothing to do!
* Married student body - There are a few of us, but we do exist. I know of at least two others in an MCR student body of 150 at Lady Margaret that are married. That said, several have partners, hetero and homosexual with whom they live. Many, many others have long-standing boyfriends or girlfriends.
* Living together anyway, despite the rules - Because of the lack of in-college accommodation for married or partnered students, students often live together under the radar. There is one in my college and one in my Masters programme who do this.
3. Discounts and Scholarships
* Discounts - several discounts (such as free museum entrance for 18-25s) are inapplicable to the mature student. The rail card student discount requires much more paper work than it doest for the 18-25.
* Scholarships - many, many scholarships discriminate on the basis of age. This includes the Rhodes, the Marshall, and All Soul's prize fellowship (there are not very many scholarships open to Americans here). The one scholarship that does not discriminate on the basis of age is the Fulbright, but it only applies for a year and to those who haven't lived in the country before.
* College-based - Several MCRs, especially the graduate colleges, provide parties, or "Bops" that are exclusively for graduate students.
* LDS-based - For single LDS graduate students attending Oxford, there is a singles Sunday School class, composed of a few Oxford students (seems to be 4-5 a year), Oxford Brookes (another local university), and local singles. Much of the single activities are based out of Reading, where the stake is located. Having a car or access to a car therefore becomes important. Some students travel each Sunday to the all single-adult ward in London, the Britannia Ward, which meets at the Hyde Park chapel on Exhibition Road in South Kensington. This is a strong ward, with at least 200 young single adults who are active. For married students, there are usually several married students (all now have families) in the Oxford Ward attending Oxford.
5. Living In-College with Teenagers - What can I say? It comes with all kinds of surprises, especially when one shares a bathroom or kitchen with undergraduates. It takes a lot of flexibility, getting used to foreign odors, and, for a onetime prudish LDS girl from Provo, UT, quick shock-deflection when she witnesses the undergraduate boys streaking from shower to room in little and slipping towels. My only advice here is to bring/buy your own bathrobe, dishes and cookware, smelling salts, and a sense of humor.