The opportunity's for your son are far greater than when we started. My sons first race was at 13 and the only way the promoters would let him race was if I rode with him, he is 21 now. Times have changed.
The biggest and most acknowledged series for UTV racing are, in no particular order GNCC, SCORE, WORCS, BITD.
Since your son is 12 SCORE and BITD are out, the exception to that is the BITD/UTV World Championships which has a youth class. If you're serious I suggest attend that race next year, and since you live in the middle of no where when it comes to any of the major series I would look into GNCC. I have no idea what they offer but with UTV sales exploding the race promoters are making classes to cover this growing area.
Next would be WORCS.
Until then enter him in any local UTV race you can find and read the bigger series rule books so when he/you hit up a big race for the first time you will have an idea of what to expect.
Good thing you said you were willing to travel...have fun!