Hey there - I'm 31, not in the best of shape but not terrible either. Probably 20-30 lbs overwieght to be in perfect shape. Its been about a year since I rode, and even then just sporadically. I'm not that great on a bike but I know the basics - not much more. My goal eventually is to trail ride - mountain biking.
Should I try to start on trails or roads? Or just around parks and such? When I get out on a trail I pretty much walk half the time, very discouraging. Hills are even worse, lol.
Thanks for any advice.

Check in your area for local mountain biking clubs. Such clubs often have novice rides with leaders who will help instruct you on the techniques needed for mountain biking.