Can a 20 year old boy get in trouble for dating a 15 or 16 year old girl if there is NO sexual contact involved?

Can he get on trouble? Probably. How long do you think it will take until there is sexual activity? Even without sexual contact, he still runs the risk of "contributing to the delinquency of a minor" (which is a crime) if someone accuses him of supplying or enabling the young girl to have access to cigarettes or alcohol.  

No, but the 20 year old boy should be extremely careful.  There are a lot of people in prison for things they said they didn't do, but someone else said they did.  And they had better be sure that they know what sexual contact means.  PA defines indecent contact as "any touching of  the sexual or other intimate parts of the person for the purpose of arousing or gratifying sexual desire, in either person."