You asked:
At what age do you think kids should be expected to play football on the park?
So if this is your question, the answer is subjective. My DS7 is allowed around the corner on the field of if he is with his brother (aged 11), but I'm actually still uneasy about that. He cannot go to the field if just with his 7yo friend from over the road.
Probably by next summer (DS will be 8 nearly 9) I might start letting him and his mate play footy on the field on their own.
Until then - they'll play in front of our house or in our gardens.
They can be out here all day at weekends on a dry day
Being a dry day does not make grass less muddy. Do you have experience of slide-tackling-football-playing children? Churned up, muddy grass needs about 3 or 4 weeks of dry weather to fully dry out and not be muddy.
It being "a dry day" does not mean the garden will be fine for football. Several weeks of hot, dry weather and it will be. Unlikely at the beginning of March.
I don't for one minute think they've damaged anything deliberately
If this was my boys [I'm beginning to worry it actually is!] I would hope the neighbour would feel they could speak directly to the boys, and they would be polite in reply.
We've had cases of balls going astray. If I see it (they are right in front of my living room window), I will go and tell them off, apologise if needed, reitterate they must keep better control of the ball. Generally they do.
Then playing all day at the weekend - I'd love that! After we've done our sports clubs at te weekend, mine would often rather play on the Xbox. I have to encourage them out there. Better they play out, than sit in front of a screen any day!
I would, however, expect them to be respectful to neighbours as much as I would hope my neighbours will tolerate and appreciate the value on children playing outdoors.