What is the maximum age gap for kids to enjoy playing together

[Em2122]

Have two close together, 18 month gap and they are starting to play together, so I feel the hard work was worth it.
I wanted 1 more but definitely couldn't have the age gap that small again.
Is there a gap when the play become more like the older child helping the younger one rather than playing together.
I was thinking 3/4 year gap may be the maximum but I am not sure.

Mine are 9DS and 5DD and they are good. They dont play together as such but they enjoy each others company like to watch tv together play family board games and go on walks together to parks and swimming ect. But in the house they do their own thing him PS4 her drawing and lots of dressing up.

I have 3DD. DD1 and DD2 have and 18 month age gap. They are very close but completely different personalities. DD3 is 7 years younger than DD1 and 5.5 years younger than DD2. DD2 and DD3 play together all the time and has lots of fun, DD1 looks after DD3 needs more than plays with her. There is a completely different dynamic between them because if personality and interest. DD3 will start a club in Sept with DD1 due to her showing an interest in it, but I really hope it will help them secure a bond too and have a bit more fun together.
With that age gap too my girls all still feel like children. It works for us x

3 years between DS1 and DS2. They are 3 and 6, now the youngest "plays" a bit more they get on really well I'd say 80% of the time. The phase when the youngest just wanted to trash the eldest's toy set ups was not fun 😂