if someone say to them that you look older than your age or that you look younger than your age?? which one should be considered a compliment? 
Re: whats considered a compliment for guy?
when ur 16, older
when ur 25-30, younger
Re: whats considered a compliment for guy?
Sara is right. Up to certain age it is considered a compliment if you look younger. After crossing a certain age it turns the other way around.
FF - it would be interesting to know what brought you to asking that question. 
Re: whats considered a compliment for guy?
If the guy is older.........approaching 30, in his 30's and above, he'd feel flattered that he looks younger.
If the guy is a teenager (14, 15, etc)....he might even think it's cool that he looks older....especially if there are advantages to it for him.