why wont it let me level my dragons higher than 10? I am level 18 but my dragons cant go higher than 10...

You need this temple:

*unlocked at level 19 in the shop

Before you can level up your dragons past that lvl cap, you'll need to puchase and unlock others as you lvl-up your city.

@Shandi-L-Snyder There are 6 temples that you have to purchase in order to grow your dragons. They will allow your dragons to level all the way up to level 40.

Each temple increases in price, and in the number of neighbors you will need to build them.