Can a 17 year old be with a 16 year old?
17: It is legal for a person to have sex with someone who is under the age of consent so long as both parties are at least 14 years old and under 21 years old. A person who engages in sexual intercourse with a child under the age of 16 commits the crime of sexual intercourse without consent.
Can an 18 year old be with a 16 year old in Pennsylvania?
In Pennsylvania, it is illegal for an adult (someone 18 or older) to have sex with a minor (someone younger than 16), even if the sex is consensual.
Is it legal for a 19 year old to sleep with a 16 year old?
As long as you are aware of the risks, the best judge is you. There aren't any laws around being in a non-sexual relationship where one person is under 18 and the other over. Once you turn 16 it's not illegal for someone to have sex with you no matter how old they are.