Old horse to teach new things

Question
I'm 14 years old but I have a horse that is 18.  He is a Quarter Horse and does not act his age.  He has been a show horse in his earlier years and then changed to a trail horse for 9 years before I got him.  He does not want to act serious in trainging.  He doesn't want to learn things that have to do with showing.  He is very bad at cantering.  Last year we were in walk/trot division and won chanpionship so this year we moved up to cantering with the older kids.  I dont know how to calm him down at his canter and keep his head down, to stay collective.  I dont know how to teach him to calm down in a pattern and to teach him how to pivot.  He doesn't listen to my leg pressure either.  When we do a pattern he dances around like an arabian.  He doesn't calm down like he is waiting for me to just let him go to run.  I think he used to do barrels or maybe reinging.  He can canter in very tight circles and do flying lead changes.  He can spin very fast and almost do a sliding stop.  I want him to forget about that and start him in western pleasure and english riding.  I hope you can give me some exercises or something to help him not push through a pattern.  Thank you so much for your time.

Answer
First of all, do you have an instructor/trainer? If not, you should get one.  For his headset problem- try a running martingale or draw reins to keep his head down.  Hopefully he will learn you want him to keep his head down.  For the leg pressure problem- when you want him to move forward, first add just a little bit of your leg.  If he doesn't listen, ask harder.  If he doesn't listen when you ask him to move on a third time, carry a crop and smack him with it (or use spurs if you are advanced enough to control your leg).  This will show him that you are serious about him listening to you.  Have you ever tried showmanship with your horse?  I think it helps a lot with a horse's manners, and teaches them to listen and watch for subtle clues.  Start out with your horse in a halter + lead, or a bridle.  Stand at his shoulder, and cluck to clue him to walk.  If he starts to barge in fornt of you, say "NO!" in a firm voice, stop him, turn around, and back him up very quickly.  Then try again. When he walks next to you and doresn't try to barge ahead, try halting him.  Say "whoaaaaa", and pull back on the reins/lead gently.  If he doesn't stop, turn around, and back him up very quickly again.  Keep repeating this.  You can try trotting with him also.  To pivot, have him stand at a halt.  Keep his head, neck, and body staright at all times when pivoting (like a pencil).  Turn to face his shoulder and neck, and take a step in, while turning his head a little away from you.  If he doesn't move his shoulder, hit him (firmly, but not hard like you are punishing him- he doesn't know what he should be doing yet.  He should move his front feet over, and 1 back foot, but keep one back foot planted.  Have him take one step, then praise him and walk away with him.  Then stop, and pivot two steps, and walk away- you dont want him to get too frusterated.  Keep doing this until he can turn a 360.  But don't try to do it in one day, go very slowly.  I found that showmanship really helps a horse to listen and respond well to you.  It's worth a try.
As for getting frisky and excitable in patterns, try this on your own:  Do one part of a pattern, then halt.  Stand calmly for awhile until your horse is sure you aren't going anywhere fast.  Stand very quietly, then praise your horse.  Do another part of the patern, then halt, and do the same thing.  This should teach your horse not to rush through the patterns, like it sounds like he is doing.  He also might be nervous about the pattern, and he is just trying to rush through it because he doesn't have enough training to know what to do.  Try to take things slowly, like one little part of a pattern at a time, then gradually do more and more.  
Also, you could also try a calming supplement.  Don't get a tranqulizer, and so you know, some calming supplements are illegal at shows- always check the rules.  Herbs work nicely.  I'd recommend this one:  http://www.chamisaridge.com/horses/1/H31001
It's valerian free, so it won't drug your horse, and should be legal at shows.
For cantering:  It sounds like he can canter, but goes fast, or is off balance.  What I would reccomend is to work on transitions.  Ask for a canter quietly, relax (very important, lol), and have him canter a few strides.  Then, sit deep in the saddle, close your fingers, and say "whoaaaa" firmly, but softly.  Make sure you sound very calm, and not nervous- he can pick up on that.  Bring him down the the walk, and give him a huge pat.  Then, ask for a canter again, and canter a few more strides, or until he feels like he's about to get out of control.  Bring him down to the walk, and reward him again.  This should help with his speed problem.
Also, never ask him to do any spins, sliding stops, barrels, or tight circles at the canter.  You probably don't, but I'm just making sure.  He'll just remember what he used to do, and get into that frame of mind again- "go fast, spin, turn."
I hope this helps you.  If you have any more questions, just email me.
~Anne :)