as has been said many times in many threads beginner is a measure time not of skill. my grandfather plays every week with friends and has been playing since the time botvinnik was champion but he lacks skill and does not study. he is also not as sharp as he once was and at 1100 rapid i beat him easily though sometimes i will let a blunder pass. to call him a beginner is to not understand basic definitions of simple concepts
It is nice that you have this opinion, but that doesn't mean it's true.
The problem is of course the term: 'beginner'. Beginner can mean 2 things in chess: 1. a player that has recently started learning chess, but also 2. a player with a specific rating that falls within the group that is called 'beginner'. If in 50 years Carlsen plays like an 1000 player, he'll be in the beginner rating class.
There is a good reason to use these classes. They can be a point of reference as to what should be done to get stronger. Everyone in the beginner class blunders too many pieces. That stops them from moving up in rating class. So the advice given to these players is similar, based on their rating class.
I think beginner class reasonably ends around 1200-1400 OTB rating.
i believe it was daughtry who said "it's not over"