I've just started biking and was looking at 2 used models of trek, a 2005 model 1200 and a 2004 model 1500. 1500 is a year older and $150 more. Is it worth it, or just start with the 1200. Riding about 20 miles 3 times a week now on an old trail bike with road tires. Will be riding in a 90 mile fund raiser in Sept. I'm not looking to be fast, but I am competitive. Thanks

These are both aluminum-framed roadsters and the main difference is in the component spec. With the 1500 you're getting better "bits".
Far more important is that the bike fit you. You say you're "new" to biking; before I'd plunk down the money for any used machine I'd take an experience rider along to check out the bike mechanically and to see if it's possible to adjust it for a good position on the bike.

You may be getting a bargain; these are pretty much in the "entry-level" of road bikes, and a lot of folks will buy a machine like this, ride it for a year, and then want to move up. You may be getting a lightly-used bike with lots of service life.

I know that Im a 56 from different bike shops, maybe better to settle for least expensive and see how I do for a year like you said. Thanks for the reply
Don