I went at 36 and I loved it. It was blooming hard work and if I'd realised what I what I was letting myself in for, I'd never have done it. Having said that, though, it was the best three years of my life.
I wouldn't recommend it without any prior study though (I had some vocational qualifications and an OU course under my belt). In fact, I doubt you'd be accepted anywhere but the Open University without it. Your best bet would be to have a look at prospectus at your local college and see if they run any kind of Access course, usually run under the auspices of a university in any case.
Other than that, there's the Open University. They run courses from introductory level right up to doctoral degrees and they're well worth a look. The advantage is that you can study whilst you hold down a job - they're very geared up to this.