When I turned 35 I just remember filling out surveys and I had to bubble in the 35-44 age category instead of the 21-34 or 30-34 and somehow I felt old too. I've found that I tend to feel 'old' when I hangout with friends who are younger than me. When I hangout with friends older than me, I tend to feel 'young'. Not sure if that will help or not. I'm currently 37 and I don't think of myself as old though I may do so in a few years.
As for the weight issue, I'm no help there as my weight tend to goes up and down plus or minus 20 pounds depending on the season. Hang in there bud. I've watched chub porn online and there are guys who look like they weigh 300+ who still get laid from apps and what not!