Conversation so far:
When was Kermit born?
According to this fictional biography, he was born in Leland, Mississippi alongside approximately 2,353 siblings.
Where was Kermit born?
though a 2011 "interview" on The Ellen DeGeneres Show has him state that he was from the swamps of Louisiana.
Does he have any siblings?
2,353 siblings.
Who are his parents?
CANNOTANSWER.
Did he leave Mississippi?
at the age of 12, he was the first of his siblings to leave the swamp, and one of the first frogs to talk to humans.
Does he go back home?
According to The Muppet Movie, Kermit returned to the swamp, where a passing agent (Dom DeLuise) noted he had talent.
Is there a movie about his childhood?
2002 film Kermit's Swamp Years.

Question: How did he meet the other Muppets?
Self-contained rewrite: How did Kermit the Frog meet the other Muppets?