Hey Op
Both my boys are Sept babies. My eldest (10) was born 2/09 and my youngest (7) 15.9
Have to say I'm very 50/50 on this subject myself (both are in appropriate years for age as per usual process). Both my boys are very advanced for their age / school year and are country miles ahead of their peers academically. Which is great in many ways BUT I have also seen the negative to this and continue to do so. As they are so ahead they tend to finish work a lot quicker than the rest of their classes and this can cause some issues with them becoming bored and fidgeting/swinging on their chairs etc so I have an ongoing battle with the School to keep them occupied and learning. I didn't notice too much of a difference until year 2 with my eldest though and my youngest I knew what I was looking for so I become aware in year 1 with him. It's taken to this year fully (year 5) with my eldest for the School to document keeping him occupied and have now started to do this he is also taken out from his class maths lesson for "greater depth learning" once he has completed his usual work and had it checked. This has been great for him so far after a rough year last year with a (useless) Teacher. I'm fully expecting to have the same with my youngest now too so I will be pushing for him to be encouraged and pushed with him capabilities.
The other negative I have started to notice with my eldest the last 6 months is, he has outgrown some of his friendship circle, he is nearly 12 months older than a lot of the children in his class and he finds them to be immature and his interests don't always align so this was a bit of a bump in the road.
On the whole though I just think that it is luck of the draw with the School you send them to and how well your child performs academically & socially in order to get them to push the child and engage fully with them. The Education system in state schools is fairly rigid in my opinion in the UK but that isn't the Schools/Teachers fault and I guess unless you can afford to send them to Private School it is something you are stuck with.
As for success on getting your child in a year early so to speak I haven't heard of this even being considered, I think it would be beneficial for some children but I feel if it was an option it would be something that would need to be monitored and a way of assessing each child on a case by case with criteria to be met.
For my eldest I think he would have been fine if this had been an option, however, my youngest I'm not sure on as I think due to Covid it affected his social skills somewhat so he benefitted from having the pre school period.
Ultimately though all children grow and learn at their own pace and make their own way eventually. If their bright they will flourish regardless and if they struggle then they will find their feet and any extra support can be brought in.