Yeah as long as you have the stock reg on the grip frame, you're fine. Just make sure you get the right VA. Older style RPMs are metric threaded (like Spyders), newer RPMs have standard threading.
On a side note, good job out of you for getting you son involved. My dad started me in the sport when I was your son's age. 20 years later, I'm still involved. I plan to do the same for my kids.
Interested in a Trinity Ion trigger frame. Shoot me a pM.
Ion XE: Custom grip hump, VP Sythe trigger, New Designz 03 Shocker snatch grip, Dust black Warrior feedneck, Hybrid gloss black clamping ring, Evil Detonator reg, CP on/off, CP 14" .689-bore Classic barrel, dust black, Blackheart board, Virtue EZ-On, Virtue eyes, New Designz Pro EQ bolt, Eclipse QEV, Kila magnetic detents, Dye gauges, Hybrid grips, finger pads removed (SPD TonTon Shocker grips in the works)