I would not stress about choosing an amp for these Speakers. They are such an easy drive I would not stress anything decent that pops up at your price will do just fine.
I have a pair and I am driving them with a Line Magnetic 211IA Valve Amp.
When I spotted your question as a matter of interest I connected them up to an old Teac BX300 35w pc S/State integrated from the 80's. Listening to them at the moment on that Teac.
Think I will sell the Valve amp and put the money in the bank.
They do indeed sound better on the Valve Amp. But that is only to expected Klipsch's and importantly myself, prefer valve amps. But believe you me there is not much in it, such forgiving speakers, great all rounders, I love them.
Letting a 12 year old loose with a Valve Amp is looking for trouble. If the lad is anything like me at that age he will burn the house down or electrocute himself or his siblings.
These are mighty fine speakers and are keepers and a good foundation on which to build a magic system. Magic bass he will drive his Parents mad.
Any S/state Integrated will do just fine to begin with these speakers are not fussy. Will do the Job on small watts so no need to break the bank. Only suggestion perhaps one with a warmer signature like a Yamaha would suit them better.
He is 12 I can only imagine what he is going to listen to. does it matter what amp you get?
Put them in the corners they like that, and the Lad will Rock the House Down. As for his parents neighbours, that is another matter.
They go flippen loud without any sign of distress.