That is sort of silly, IMO.
Gabriel was not human. Gabriel was an angel.
Paul also wasn't talking about Jesus - who was and is truly man, with the marks of nails in his flesh.
So that's two exceptions right off the bat.
But the original posters use of the scripture was excluding all these obvious exceptions. "All have sinned..."
Absurd use of scripture leads to absurd results. So if a piece of scripture seems to be saying something that cannot be true: it isn't. We're just reading it wrong.
Mary is also an obvious exception to the 'all have sinned' line. Remember the words spoken to her by the Angel Gabriel.
Chaire, Kecharitomene
She was Full of Grace. She was without sin.