My 10 year old son (Pretty big fellow of 150cm, for 36 kg and quite strongly built (windsurfing in summer, bouldering/climbing in winter

) is surfing now on inland lake for 12 months and handles a
Bic Techno at the club quite comfortably with a 3,5-4 sail in 2-4 bft winds.
Can beachstart .
I'm looking to buy his first own board and wonder what would be the best option looking for the future :
Buy a ProKids Go or go for a Standard Starboard Go of eg. 111/122 L . I just wonder what importance this difference of volume will have for his relative weight.
It would be his first experience with a no dagger board .
thx for any constructive comments.