Well I'm 18 and I'd put on blue, it's my fav color. However, depends on the shade since it may look different from pictures.
I think that shade of blue is fine for guys. It feels sorta neon blue which is kinda cool for a laptop. I wouldn't mind having it for myself.
you should have got a Black one
It's probably not worth asking here as most people here still seem to think that White iPhone = Girly/Gay
My personal opinion? Whilst I'm not a fan of colored covers, I see no issue with the one you posted being for a girl or boy - it's a fairly "neutral" color...if that makes sense.
I think it looks fine. It depends on his personality. If he's outgoing then he can use the color as expressivity/accessory. A shy guy might want something more neutral, like gray or black.
I would use it!