Kang Seung Jae already wrote that
>an informal version of san used to address
children and female family members.
You could use it to refer to a male child. And of course there is a sort of teasing colour in the example you gave.
Gengerally speaking, you cannot say -chan when an adult man is at issue. It is a symbol of childish/girlish cuteness. You know, infants cannot pronunciate the sounds well. They often confuse [t], [tS] and [s] (sorry I cannot write here the phonetic sign; [tS] means ch of choke). -chan has its origin in the baby talk of -san, wrongly pronunciated as [tSan]. Therefore, it implies the infantile nature of the person. Boys and adult men regard it as insulting, while females take it positively.
Associating childishness with girls is undoubtedly problematic from moden gender sense. But please know that historically Japanese culture has often identifies the infantility with cute atractiveness. See, for example,
Sei Shonagon, The Pillow Book, paragraph 151 - I think it explains some parts of the root of MOE.