melev-
the bar is 36" inches so I'm probably 40" at my max height. I tied it up for first. I was skating as fast as I could. You have more momentum to get yourself higher the faster you go with almost any trick. Your son has a great start with that just tell him to keep at it.
Right now the highest ollie is set at around 44.5" from flat. I have a feeling I can do it but my knees need another surgery so we will see.
TIMMYE-
As for helmets at any skatepark I use my helmet but out on the street there is a higher risk of breaking your wrists, arms, ankles, and knees.