Can one have social phobia their entire life, meaning, from a very young child?

I've heard that it usually occurs around puberty, but does this happen even to outgoing children, or does it usually occur to people with shy temperments?

Is the difference between people who have the SA disorder and who are just naturally VERY shy (though they fit all the symptoms for the disorder) just that the shy people have had it since they were born and the people with the disorder have had it since puberty?

I'd appreciate any thoughts on the subject.