There is basically a limit to EVERYTHING! Nothing can exist without a limit. And that includes love, as when love goes without a limit it can become an obsession, and that is never a good thing. But that is rather if how much love you can give and receive...
When it comes to the elaboration you gave TimidDeer's request for clarification, then the only limit I believe is may be age, as young children do not experience love the way adults do, however when it comes to "he is 80, she is 20" I may frown a little, but hey, if she really loves the guy and he loves her, who am I to judge? As long as I can be sure she isn't a golddigger (but that has nothing to do with love, merely abuse of love). When it comes to love between members of the same sex...
Now I am a straight guy, so for me only a member of the opposite sex (that would in my case be a female) can do for me, (nothing someone says before the word "but" really counts), BUT if you are a guy for whom only a guy can do, hey then you are the one who has to see him everyday, who has sex with him, the one you gotta make happy and the one who has to make you happy. Not me... Would you criticize me if I got a girl-friend you think is downright ugly, when I am the one who has sex with her... the one who has to make her happy, the one she has to make happy and not you? Would be the same thing in my point of view....
And when it comes to religion... You need to adept. If you are religious and would be my girl-friend (this is NOT a proposal!), I would have to accept a bit more bible in my life, and maybe you need to accept a bit less bible in your life. But if I would date a Korean girl, I would always be Dutch and she Korean, but if I can be tiny bit more Korean and she a bit more Dutch, it doesn't have to be much, anything is possible, right? So in that sense, no limit, as long as we can speak of "love".
In the end love is love.