I'm 34 and just started riding regularly for the first time since I was in middle school. It's been great for me. I had chronic knee pain which has since gone away since I started riding. In 3 months I lost 2 pant sizes and feel stronger and more energetic. I went with a Surly Steamroller. I wasn't totally sure if I wanted to go fixed but I gave it a shot and really love it and picked it up almost immediately (after a little practice on an empty playground at night so nobody could watch me forget that I couldn't coast). There should be nothing wrong with switching to straight/riser bars. I personally really like pursuit bars because straight bars don't feel very good for climbing out of the saddle on hills.