Pros and cons to the debate.
In Germany, my younger cousins weren't allowed to play full size untill 15 years old as was the norm over Europe, this was over 20 years ago. The confined space encouraged closer control and use of smaller goals improving accuracy. At 15 deemed of correct size and ability to cover the larger area with ease as a natural progression. Perhaps why we are years behind in development?
I suspect some of the kids development in formative years is 'coached out' of them. My son has moved up to 11-a-sides this year, luckily under the supervision of decent coaching. Emphasis based on passing through, they aren't rewarded for going long, hitting it the hardest, win at all cost unlike others. For example, playing Celtic on Saturday past, the opposition coach encouraged 'aiming high' when in a scoring position. They did once at 12 nil in a 14-1 drubbing! In a youth system with the resources available at their disposal, I'd wager Mr McCart wouldn't agree...
In the interests of 'traditionalism', the move to full size is favoured at this age. Seen enough and spoke to many in the past few weeks, coaches despairing as kids threaten to give football up as others inflict defeat after defeat by double figures by aerial attack. 10 & 11 years old lost to the game? Nobody in power understanding of this? The average 10/11 year old is half the height of the goal equipment at best, where is the development in technique in both defence and attack?