12 yr old son, want to buy him his 1st mountain bike. My budget is probably maxed at $350. I want the lightest bike I can get, but beyond that I don't know much else. I do know I don't want full suspension, just in front. One bike shop recommended Trek 3700 for $279 or 4300 (don't remember price) or Specialized Rockhopper for $369. Another one recommended Specialized Hard Rock XC for $370.
Also don't know what frame size to get. The one shop recommended 16" after seeing him, saying he'll grow into it but he was on hip tip toes straddling the bike which I don't want. I'm thinking a 13-14" but don't know.
Any advide or bike recommendations would be appreciated.