Your boy has good taste lol.
If he's still a growin' boy the Mathews/Mission "Craze" or "Riot" might be worth a look. Huge adjustment in both draw length and weight.
If he's about done growing or You dont mind buying another cam when he out grows the draw length then look for single cam bows, like Heli-m, Z7, Z7 Extreme, DXT, Drenalin, Outback, Hyperlite, Switchback, Switchback XT. Or older models like LX, MQ32, MQ1 SQ, SQ2. You will see some Reezen 6.5 and 7's. They have an agressive cam and questionable riser strength. The others mentioned will be better choices.
You will also see bows like, Conquest, Conquest 2,3,4, Conquest Triumph, Rival Pro, These and a few others are longer axle to axle and more target oriented.
The MR5, MR6, MR7, XLR8 and Monster are the hotrods of the Mathews/McPherson company and require a little more maintenance to keep "em running at peak performance. They have an agressive cam. They will be a little longer and weigh a little more than the other bows. When set up properly they will flat out shoot! But probably not the best choice for a boy.
My personal choices for a pre owned hunting bow would be the Z7 Extreme. Shoots like a dream. short axle to axle, seven inch brace height, smooth draw cycle and plenty of speed. DXT for the same reasons. And the older Switchback XT. Butter smooth on draw cycle. Was a great bow.
Regardless of what one you choose, get the boy measured for draw length. And find out what poundage he can comfortably pull. The bow must fit and fit just right or he will never shoot it as well as he is capable of. Hope this helped and good luck in your search.