OK,
Here is the deal. I have a 14yr old that wants to MT Bike race. There are only a couple races left in the season then there are a few Cyclocross races. I know....NOTHING...so I apologize for sounding like an idiot. My question is, for a couple of local races, can you take a cheap used road bike or a decent vintage road bike and create a serviceable Cyclocross racer out of it, or do you need a 'cyclocross' bike. we are talking Jr 13-15yr old class.

Thanks.

Yep, the vintage road bike ought to work decently, especially if it's more than 10 years old it'll likely fit wider cyclocross tires. I'd say go for it.

Does your kid then have a mtn bike? If so, just use that.

He does have a mt bike...can you do it on that? I thought it had to have the drop handlebars etc?

Naw, they'll let you ride any bike. It's just a bit harder on a mtn bike.

Just make sure if he has bar ends you remove them. Most races wont let you run them.

Off topic but why is this?

spear factor.

bit like the 'running of the bulls' in Pamplona.

Makes sense

along the same lines, make sure your drops have plugs in them.

Don't bother with drop bar conversion, the project will get expensive fast with new shifters, brakes, stem etc, not worth it. Use it as is, or you could replace the suspension fork with a rigid one to save some weight, and maybe switch the brakes so the rear is on the left lever, not critical but helpful when he starts learning fast dismounts to be able to slow with just the rear (no weight on the saddle = endo) You could also lighten the wheels up with the narrowest 26in tires you can find, but again, not necessary. The main message, that should be communicated clearly to him, is that you can race cyclocross on just about anything and be competitive. More than other cycling events, it's all about the engine and the skills...

There is a Junior race at my CX events, and I don't think I've seen a single "true CX" bike in any of them. Everyone is running hardtails, with the occasional double-boinger thrown in... much like shoes, I think it's too expensive to buy a 14 year old kid multiple nice bikes that he will outgrow in a year or two.

when i was racing cross in upstate ny there were a bunch of kids on little redline cross bikes. some of those kids had serious gear!