Is it ok if a 37 year old man is dating a 16 year old girl?

Probably not because (yep there is a reason) the 38 year old is at a different place in their life then the 19 year old. They are faced with issues and experiences that the 19 year old is not. The 19 year old is in the same boat. On the road of life they are just in 2 different places. I suggest looking at the relationship and asking yourself "Is this a true partnership?" most likely it is not equil on either side.