Hi itdts027
Congratulations to you son for cracking windsurfing and to you for your effort !
I,m a great fan of the Ezzy rig packs,both my kids had their first experiences in windsurfing on them.
The 12 year old kids who windsurf at Sanctuary point use mainly 2 sails ,3.0m and 3.6m, for 10 - 20 knots conditions and 2.5m for 23+ knots .
They are 10 kg heavier than you son so I think 3.5m is too big. My 8 year old uses 2m-2.7m sails in that wind range and still uses a 1.5m for 25+.
For kids 12 and under the mast is the most important component of a good kids rig.
My kids have used all the above mentioned rigs and quite a few others as well.
Your real issue is going to be finding if any are actually available to buy.
I have PM you my phone number if you would like to discuss further.
Brett
The rig you son is using is a Prolimit grommet,they made 2 models and yours is the power rig.
PS It must be windier where we live

that or your son is following in your footsteps and going to be a formula sailor.