Kids don't use an 8.5 they learn on kids rigs as the video shows and the weight of the board is not relevant, as you know smaller boards are for advanced sailors. As for age I think they can start as young as the junior dinghy sailors 7 or 8 yo or when they can pull up a rig.
The plan with junior recruitment is structured similar to dinghy sailors ie
YA has a tackers program that introduces kids to sailing (perhaps we can call juniors windsurfers helitackers), they then progress to the opti green fleet which introduces them to racing on a inshore course, kids then progress to full blown racing out on the full size courses.
We want to follow a similar formula as it works here for sailing and for windsurfing overseas ie for new recruits the emphasis is on learning, kids that have the basics down then do small inshore course, it may be upwind downwind or even a simple reach to a mark 50mtrs off the beach and back, then when confident they can progress to the full course even with a smaller rig than the class rules allow and finally they progress to a full techno set up and start racing for sheep stations. In the early stage I think any gear will do its not important, only when they start full racing will it be nessecary to move to a techno.
Having little kids sailing with big kids will naturally inspire them to want to do what there doing.
The kids currently doing techno are doing approx 70 races a year, with that amount of TOW you will be surprised how quickly they progress, from the time my son (14yo) stepped on a board with a kids rig to doing his first regatta on a techno was about 4 months, he didn't finish any race but that doesn't matter, within a year he was racing at Hawks Nest in the Formula Down Under Pro. The kids learn so fast it will put you to shame.