I don't know how things work in Ireland, but if you can find a good trainer who will let you be their "apprentice" of sorts, this may be a start. Work under them for free for awhile. Then when you can prove that you have the skills to train, perhaps they will let you take over beginner lessons and earn some cash to save up for your own horse. Maybe you can get someone to video you working horses (riding, lounging, etc.) and send that to some of the big name trainers and ask them if they would be interested in helping you further your goals by letting you shadow them (again apprentice type work).
I don't think it's a childish dream at all. Good Luck!