You could try it, I managed to convince my parents to rescue Gemma in 2008(i think) who is now my own [the owners GAVE her to me a few weeks ago
We rescued her because if you were to call her obese, that would have been an understatement and she's an awesome little girl at 38" and 6yrs old.
Because I wasn't going to be allowed to break in a full sized horse I started breaking in gemma when she had lost the weight to safely trot and canter without hurting her back. [yes I got on her and still do but I was very very light at the time and it was only for 5 minutes at a time at the most]
In my experience they are pretty easy keepers, although gemma seems to gain weight upon hearing the word "grass"
They keep you on your feet a bit more than full sized horses though because obviously you need to keep them fit and you can't very well ride them like you do a normal horse.
So [god help me] I do inhand jumping with gemma and we walk down the road and go swimming etc etc etc. <an upside to the mini is that they cost a little less to feed, although gemma got laminitis after we got her (during her diet) and now pays for it during spring by only being allowed in a dirt paddock with hay and feed until the grass sugars have leveled out again... dang dairy pasture :roll:.
They seem to be easier to teach tricks etc than full sized horses. Gemma will bow and back up and lay down a lot faster than my full sized horse will. (like with gemma I just lift the reins up and she backs up, with bubbles you have to full on lean against her chest and push her backwards while saying back... she just doesn't get it:roll:)
I'd say give it a go, but in trying to do so make sure your parents know that you do understand what you have to do with them etc like the excercise and feeding and teeth and hooves and worming etc.
*oh btw, miniatures need dental work slightly more often than bigger horses due to the fact that they actually have full sized teeth, not miniature ones so they are more prone to crowding etc.
This is Gemma the day we rescued her Copy of Pictures 006.jpg
This is her a few months ago 31.jpg