For my two cents worth, no man of 21 worth his salt would get involved with a l6 year old girl. That his father is a teacher makes it even worse - his father should have made it clear that you don't muck about with schoolchildren....

However 'nice' he is, this young man is exploiting the niaievity and youth of your daughter. He's bad news.

All the best - Julie

PS - don't suppose your older daughter could influence her sister could she? (probably counter productive, thinking about it....)