Muay thai has a vastly different approach to punching than boxing because the kicks, knees and elbows playing but there were plenty of good boxers who crossed over from muay thai or kick boxing and became good contenders or champions. Most of the Thai dudes who were and who are currently good at boxing started out as muay thai guys at some point of their career. You don't really see it at them maybe their stance is more square. An dof course most of the time they are tough as fukk
Boxing is a sport that is easy to learn at a basic level but hard to master with that said there were plenty of boxers who became good or very good just with a few years expereince behind their back, so it's not set in stone that you have to do it for x years at least to be this or that good, I guess it depends on dude's natural ability and on how serious he took boxing how good he could become in those 11 years of doing it.

Some ppl progress more in a year than others in 3 because they are just more enthusiastic about it, train more, have better ability, etc...
It's not a sport like swimming that you have to start as a child or else you're fukked. Look at guys like AJ or Wilder, they started boxing at age 18/19 or something.