I live rurally so upto 11/ 12 yrs old they do not venture pass the front gate, we have 3/4 of an acre plus a mini pitch beside that again.
Many considerations for me:
Age and maturity
Safe area
Passing traffic, is a main road with plenty of traffic or is it just local traffic
Are there boundary walls, pick a point they don't go past
Can you see them from a window
Are there friends in the area and are they well behaved
Have you neighbours, the village rearing a kid kind?
Bottom line for me is that while they are safe and should have free reign to explore, there ARE way more perverts and paedos due to online porn, no moral compass anymore and a lack of supervision from the 'village'. So I wouldn't let mine out to play unless I had peace of mind regards their safety....call me a helicopter mom if you want, I don't want my kids buggered.