Im old (37) and in my first year, but it's mostly irrelevant in the grand scheme IMHO. Your outputs will be the most important variable in your success. Most uni's run international student funding, so look around. I'll plug my own Uni they have a pretty big Environment department:
http://www.york.ac.uk/environment/postgraduate/mphil-phd/
Also, strategically speaking, you may want to look at a somewhat interdisciplinary vein of study if you are trying to set up good work prospects in industry / academia in the future. By that I mean throwing some social science into the mix (usually Economics or Politics), which is a good foundation for development oriented work, more specifically sustainable development, which is very "sexy" right now and attracts piles of funding...anything sustainability related to the climate really.
P.S. The process for me to go from "being interested" to "being on campus" took about one year (searching, sorting, applying all the while putting together a decent proposal.) so get cracking ;)