Maybe you won't believe it, but every trader, even the best ones, was new and beginners at some point.
Of course they were that's why this advice it's a bit weird!

How to you stop being a beginner in something if you never start doing it in the first place?
Everyone is a beginner in something, trader, gambler, nurse, construction worker, astronaut you name it, everyone had a time where he had no experience but he tried it.
Imagine how the world would look if we make a rule like nobody who hasn't operated on a human before is allowed to operate on one, in 40 years from now there will be guy able to do a surgical interventions!
A more down to earth advice would be to not try to trade more than coffee or cigarettes money while you still don't know what you're actually doing, but keeping away from trading completely will make you one forever newbie!