Matt,
The "rapid growth" is very relative: this one must be in its fourth year I think. And from the top of the rock to the top of the tree, it's less than 10 cm (less than 4 inches).
But taking very young specimens gives the pleasure of being able to shape them, cotoneaster branches are not that easy to bend. In this case, it also makes it possible to display the roots on the rock more nicely.
The rest is a question of patience: you are young, you have plenty of time ahead of you. Think, in fifteen years time, you'll be able to say "Yes, I grew this prize-winner from seed. No, it is not for sale."
