I'm going to tell you what I told my mom when she was debating getting her new bike: If you LOVE your bike, you will want to be out riding constantly. (so that deals with your point #1 about being frugal (and also point 4 a little))

#2: Test ride lots of bikes, have fun with it, and then make a decision. You may have second thoughts or subsequent bike envy, but everyone does at some point (I think.).. that's what accessorizing is for! With some minor tweaks you will make whatever bike you get "your own" and will love it (n.b.:this process may not be cheap but it will be fun).

#3: Bikes are meant to be ridden. And as I've been telling myself lately since my bike's sandpaper incident, you can always repaint.

#4: I don't think you're old, but seriously, you can't take it with you... so have fun and enjoy life!