How long does it take to qualify as a referee? I ask this as I cannot see why they couldn't have started a training programme as soon as they knew VAR was coming, where they taught the laws and you became a qualified referee at the end. There would be thousands (at least) of people who could learn the laws and do the job, but don't want to run around fields getting abused and attacked as part of their training.
Qualify to what level? Each level has a higher standard. You can qualify to be a grassroots young kids ref in a few months (Grade 9/8).
You spend a season at each level for the most part (at least for grades 7-4), before moving up, if you're a good ref. Here is the pyramid in England:
Level 1 - National List (English Football League and English Premier League)
Level 2a - Panel Select (National League Premier)
Level 2b - Panel (National League North and South)
Level 3 - Contributory (Contributory Leagues)
Level 4 - Supply (Supply Leagues)
Level 5 - Senior County (County Leagues)
Level 6 - County (County leagues)
Level 7 - Junior (Amateur leagues)
Level 8 - Youth (Junior Referee below age of 16)
Level 9 - Trainee
So to get to the depth of knowledge required to understand the LOTG at Premier League/UEFA level, would take a few years. It's just like the coaching badges - from the bottom of the pyramid to the top (A/Pro Licence), the topics and information don't change, it's just the depth of information and the expectation of how much you're required to demonstrate a mastery of, that does.