Can whistle register be done by everyone who practised?

Yesterday my brother and I practised whistle register,my bro can't sing very well but he can do the whistle simply but not that high,and I can sing upto 3 Octaves but I can't even do the whistle register,doing a whistle register is my dream,Why?Is whistle register can be done by someone only who are special,please tell me how to do it :-( Serious answer only please.