This is nearly exactly the same story that happened to my DS. He started reading just after he turned 4. Someone popped off at school and asked him if he was memorizing books because 4 year olds can't read. He totally internalized that and literally refused to read until his 5th birthday. Then he just exploded with reading. We had tried to talk to him, encourage him, beg and bribe him but nothing worked. He would say "I can't read until I'm 5" over and over.
He also has had some anxiety issues. We had to bandaid his fingers after he had dug into his nails so badly, they were bleeding in the middle of the nail. Mostly, we just try to talk to him that everyone is different and point out that some of his friends are much better at running/hitting/biking etc and he just happens to be really good at math and reading. We say that everyone has a "thing" and this is his "thing". It seems to have helped him not compare himself to others as much and he's slowly learning not to internalize others' nasty comments. I tell him "they're just jealous because they don't know what their thing is!"
