That's a good question. Since a father can cut a son out of the will, and has no obigation to give anything to an adult child, I do not understand why this guy thinks he can force Shatner to give him anything. But the kid was born in Canada, maybe Ted Cruz can answer this question for us.
I suppose one could make the argument for the support from 0 to 18. But I am thinking something like $20K per year - $360,000 say $500,000 AT THE MOST.