Maybe they are drunk, maybe they act in the heat of the moment. Basically Han fucks Luke (Luke is not so inexperienced as he seems), and afterwards Han is worrying about the age difference (since it is about at least 10 years if I am correct). He thinks that "Luke is still just a kid, he shouldn't have done with him, he is too innocent" etc. Luke reassures him, that he can decide what he wants, and he wanted it with Han.
Han/Luke - Han thinks Luke is too young for him, feeling remorse after sleeping with him
Basically Han fucks Luke (Luke is not so inexperienced as he seems), and afterwards Han is worrying about the age difference (since it is about at least 10 years if I am correct). He thinks that "Luke is still just a kid, he shouldn't have done with him, he is too innocent" etc.
Luke reassures him, that he can decide what he wants, and he wanted it with Han.