They're both grown, why would that be a problem? It's his business, he can date who he wants. It seems like people are obsessed with who dates who and it's getting old. Just let them be. People date, famous or not. Why is it a big deal? Who cares? As long as they're haooy, that's all that matters.
I think it's appropriate - I mean, why not? Neither of them are married. Neither of them seem to be great brains so they would be able to have a conversation or two. They work in similar fields (entertainment). I imagine it would be hard for celebrities to meet and date 'regular' people. How would they encounter them in their rarified lives?
Anyone should be able to date who ever they want to date. It does not matter if the situation is appropriate or not. It is understandable if they have to be careful who they come into relations with since they are very popular and it is difficult to have privacy. However, people should not be determining what is appropriate for them to do themselves.
Is this seriously still an issue in today's world? With all the problems facing our nation, people are worried about two rich people with a bit of an age difference between them dating. It's not like either of them is underage or being forced into the relationship. I say let these two adults make their own decisions about who they see.
In my opinion, we do not know the true motive behind either Justin Bieber's or Kourtney Kardashian's reasons for their relationship. While the age difference of 15 years is fairly substantial and some would surmise the hook-up is all about revenge on the parties' previous partners, we cannot know if either or both are benefiting from the relationship in a positive way.