Great Instruction
Great instruction and self-study are probably more important than the boat size. I learned to sail on a Sunfish in my early teens and sailed one until my early 20's. I stayed out of sailing for about 20 years until I bought a Mac 25 last summer. I've seen people who started out as I did and other's who trained on a sloop-rigged rental or school boat then bought a 30' as their first boat.You can learn on anything. The important factor is getting to a level comfort, competence, and confidence in your abilities. A good instructor, asking questions, and reading as much as you can will really determine what is the proper size.You might want to consider how much of an initial investment you want to put into it, since there is the chance you might find sailing just isn't for you. Lots of people have learned on Catalina 22's. They are relatively simple boats, have a stable re-sale market, and have many of the same controls you will expect to find on larger boats. I'd almost call it the Cessna 152 of sailing. My advice to a first time buyer is to buy something which is already pretty much depreciated out and in good condition. No matter what you buy as a first boat, you are going to develop boat-envy or find things that are inefficent to you on your boat and want something else before long.When I wanted to get back into sailing, the first boat I thought of was a Catalina 22. I was thinking I would outgrow it in a year and look for something in the 25' to 27' range. About the same time, a Mac 25 became available at a smoking price and I figured three feet wasn't going to make it any more difficult to sail since they are rigged similar, so I bought my second boat first.