it’s not just going into school that needs to be considered but also them leaving school. This is often not considered and children can be going to uni at 17 which can be hard.
Is this a quirk of the scottish system? In England an august born child would turn 18 at the end of 6th form and would not be going to uni aged 17.
play is not as encouraged as a learning opportunity.
For me, its not that play is not a learning opportunity. Of course it is. But its what you learn. You can learn social skills, problem solving, creativity. But you don't get anywhere near the same academic learning from play that you get from formal education. Not all play is equivalent either in the potential for learning. Studies will tend to focus on "perfect" environments where students are guided to ensure they challenge themselves enough, explore a range of different resources and develop skills further. In reality, if a child plays repetitively riding wheeled toys around a garden and rarely chooses to explore other materials, no, they will not pick up any pre literacy or pre numeracy learning. There will be a point where there's little novelty or value in the physical skills they are practising doing this.
Schools & the education system were really set up to focus on academic outcomes. The teaching of skills like reading, writing and maths, and the acquisition of detailed knowledge in areas like science, history and geography.
The assumption being that characteristics like resilience, decision making, negotiation, social interaction, emotional regulation, are for parents to have responsibility for and are less within the scope of school and that there's plenty of time outside school for play.
Parents overscheduling childrens lives is as much of an issue as the school starting age. There's time & learning capacity for school AND play.