you look like a boy - you don't look like a man - there is a difference between the two! For example there are men who have that chiseled face, just that look that makes them look older than me! This is the only way I can put it for now. Boyish is Leonardo Dicaprio or Zac Efron and manly would be Gerard Butler! To each their own - I think boyish looks are good to a certain extent but to some boyish also means gay so everyone thinks differently!
I would say 'boyish' is a good thing! it suggests a general 'cuteness' but also means that you look young etc. Looking masculine is more rugged, facial hair etc. Boyish can also mean you look gay/girly though so it really depends on the individual. I think both types of guys can be attractive.