Yes. A pro will do 20-28k or so a year, so a decade as a pro, plus a few extra years would do it.
It sure helps when all you have to do for a living is ride.
Doing half that with a full time job is something. I was really pleased when I cracked 10k the first time.
I did ask Jack Eason about the 300,000 mile club. He was never interested in it but reckoned he'd "Easily done double that, at least 700,000." He was riding about 22k a year then. Being retired with a boat on the Thames, living in Waltham Cross and having an Audax habit help the miles too.