I started on a CB450 and it was ok. You need to be mechanically inclined though, you are looking at an old bike here, you can't expect it to work flawlessly. Check insurance, unless your family has too much money and is willing to spend an exhorbitant amount on insurance, you are probably better off saving your money for a few years before you start riding. It is hard to get ahead in life when all of your money gets used up on toys.
Some good bikes to start with if you want to ride instead of wrenching would be a ninja 250 or CBR125. The bike won't cost much more than an old bike to buy (especially the 125) and you should enjoy relative reliability. If the increased upfront cost is too much, unfortunately you will have trouble affording this hobby for a while. I still think that with the high insurance rates in Ontario, people starting riding before they are about 20 is crazy. Riding is great, but you are setting yourself back for the rest of your life.
Good luck.