First, I'd check with the tournament organizers as there may be restrictions. My sons compete here in NY in several organizations and many of the tourneys require a minimum of 150HP.
Second, what types of water bodies are the tourneys? Aluminum is OK for small lakes but bigger bodies of water could be dangerous with a smaller boat as you don't get to pick your weather on tourney day.
Third, what type of vehicle will be pulling the rig? Fiberglass is heavier so you'll need a car/truck with a transmission sized for the weight you are pulling. Aluminum is great for towing.
Last, it's all about the engine, many of the bass boats on the market perform well and last a long time but be wary of used engine sales and do your homework before buying. My son's last used boat had a transferrable engine warranty, for example.
Good luck to your son on the trail,
Bart