is it bad to be in 愛 with someone 7 years younge than you?

If your friend - Joy - is your age, and the brother is 8, I highly doubt she's in 愛 with him. She might adore him and think he's cute (in an "awww, look at that little kid eating ice cream!" kind of way), but I seriously doubt she's in 愛 with him. He's not, shall we say, mature enough for a 15 年 old girl to fall in 愛 with him. No shared interests, really, and it's not like あなた can have any "deep" conversations with an 8 年 old. What is there to fall in 愛 with? She may 愛 him, but she likely isn't in 愛 with him.
(Or she might just be horny...)

But, with the original question, after a certain age, I don't think there's anything wrong with a 7 年 age difference. あなた just have to be mature enough to know what you're doing, have enough similarities (both in terms of interests and like, both having serious jobs) and be willing to make it work. あなた have to care about each other and communicate well, same as in any other relationship.

(By the way, "gay" and "homo" mean the same thing. And レズビアン fall under the category of gay, anyway. あなた didn't need to say all three.)

How old are Joy and the kid?
If he's very young, yes, it is wrong.

If she's truly in 愛 with him at your age, it's creepy. However if あなた were adults, I'd say differently, my friend's parents have a twenty 年 age difference and many interesting couples in the fictional world have quite a big age difference, BUT they're adults so it's totally different there.

It would be ok if like,she was 27 and he was 20,but not okay in the situation you're talking about.Anyway I agree with r-pattz.