Haha ok I have to put a couple of photo's up to make you feel better. A few years back... I think 6 years now? My lovely wb mare broke her leg in the paddock and had to be put to sleep. To keep me busy, I leased a little QH x appy mare, sight unseen I just went to pick her up! A bit of a project horse I guess. She was 12, had done absolutely nothing other than a little bit of trail riding and never cantered.
This is her first ride:
I had no idea how to ride her! She was so downhill that it felt as though she was tipping me over her shoulders constantly. Me being a dressage nut, but also loving the challenge in training horses and improving them in front of the owner's eyes, took it as a great challenge!
It took me less than 12 months to have her working at elementary level dressage (shoulder in, travers, walk-canter-walk etc.) and she placed, beating a few lovely WB's, in 2 novice tests at the state championships.
An 'after' photo (sorry, I don't actually have many photo's of her but you get the idea!!)
I know it's not jumping, but I hope you get the idea from those that you can still train a horse to a reasonable standard with correct training ;) Go out there, get some good solid dressage work into your gelding and once he has learnt to take his weight over his hind legs, you won't have a problem, particularly as you're not aiming to leap enormous hurdles ;)