Trail bike advice

[Awakener]

Hey all, very much a noon to MTB, came off dirt bikes so family trying something new. Looking to get my son trail bike, something that can take on the single tracks, tech and some jumps as well. Happy to go second hand as only have a budget between R10k and R15k (yes I almost fell of over when I saw the price of MTB). My son is 1.7m tall and stocky, he already has a trek jack 2 jump bike for the pump tracks but with a single gear is struggling at the intermediate trails at cycle lab bike park as the climbs killing him. Any advice or recommendations would be great, looked at the specialized rock hoppers and they looked pretty good but open to advice, he is a pretty aggressive rider but not interested in xc or dh, I understand that trail bikes apparently sit nicely in the middle. Will look at hard and soft tail (we have only ever ridden hard tails) and would prefer something that has air shocks that can lock out. Thanks all 

Edited February 1, 2022 by Awakener