What sort of board did you sail before?
Longboard with centeboard or shortboard with only a rear fin.
The Go Windsurfer might be OK at first, but it will limit you to
longboard style/rig steering until you get another board.
You son can learn just as well (perhaps better than on a longboard or Aquaglide)
on the Go 151 using the center fin at first to help him stay upwind.
As soon as he figures out how to stay upwind without the center fin, he will
be on his way to shortboarding.
12 year olds learn very fast.
For you the 151 can be sailed as a longboard right at first until you get your
balance and skills back, then you can take out the center fin, put in the plug,
and have nice wide shortboard to progress on.
Might be somewhat large for 20 knots+, but it can be sailed in those conditions,
and the additional volume will be good until you learn to waterstart.