Alternatively --- think big!
I don't mean to undercut Steve's message --- different approaches are right for different people in different situations. I'm 52 and I thru-hiked the PCT this past year. 2600+ miles of hiking is a great weight loss program.
Caveat: it's not a *sustainable* weight loss program, and in fact I got used to eating as much as I wanted and then some (and still losing weight at the time). I'm back to somewhat overweight now, so I agree with much of what's being said here.

Still --- sometimes going for a big goal can work well.