Julian Lennon — firstborn son of John — is only 2 years old.That’s because the singer-songwriter — who was actually born John Charles Julian Lennon to the late Beatles legend and his first wife Cynthia Lennon — legally changed his name to Julian Charles John Lennon in 2020.“I’d always take an issue with that, because I’d always been known as Julian — first and foremost to my mum,” Lennon, 59, told The Post. “And I used to get a lot of crap for [being named John] at airport security.