You'll need it to have high Happiness/Friendship in order to evolve it.
Stantler does not evolve.
graveler doesnt evolve at a level, you evolve it by trading.
Level 20.
Level 23. 
Level 20
it will evolve at lv. 20.
Your Aron will evolve at level 32 into Lairon.
14
35
Level 27.
Level 18
It evolves at level 18.