Track and field covers a lot of different areas. If you're talking about throwing, you might want to consider the Highland Games route. The nice thing about Highland Games is that people come into the sport from a huge variety of different backgrounds, skill levels, and ages.
There are 45-year-old first-timers, and college-age kids who compete in the A divisions, and everything in between. The experienced guys are always willing to help out the newbies, and you probably won't be the only beginner in any given competition.
Personally, I started Highland Games competition six months ago. I'm 28 years old with no previous t&f experience. My throws were pretty awful in my first competition and mediocre in my second, but in my third comp I placed third overall in the C division, and took first place in several events in my division. It's all about learning new skills, growing as an athlete, meeting people, and having fun.
Now, if you're talking about running, I don't have a clue.