Hello,
I changed career at the age of 30 from marine engineer to one in the environmental field. Went to University and got my degrees. While environmental matters are high on the world agenda, the pay, especially for countryside management etc is not good. try volunteering with your local wildlife trust for a start or another voluntary group who do practical conservation work. Give you an idea if you like it and also develop contacts. getting the first job in the field is always hard.
Stephen
My official and proper job is mainly countryside manager (I own my own contracting business for countryside management with one main client) and in the summer its great, when there's fun work to be done, in the winter, it can be less so, and litter picking can get really demoralising. But give it a go and see who is out and about in your area to volunteer with to get a feel, just be warned volunteers get the best jobs normally.