No it's not dangerous to hit your funny bone because when you hit your funny bone such as on a table etc you're not hitting it hard enough to cause any serious damage.
I've hit my funny bone as a toddler and young child and older kid and even teen and adult and it never has caused any problems.
I seem to have the worst luck though when it comes to hitting my funny bone because it seems like at least once or twice a year I will somehow manage to hit my funny bone on something.
I get a tingling feeling and I don't think it's very funny until afterwards but you should not suffer any serious damage to your bones or nerves from lightly hitting your funny bone.
It happens to everyone eventually.