What age range are LEGO City sets really suitable for?

Box age ratings start at 4+ for the simplest sets and climb to 7+ or 9+ for larger builds. Verified-purchase reviewers at Amazon and Target frequently say their 4 to 6-year-olds can build age 5+ sets with adult help, while 6 to 8-year-olds can handle most standard City vehicles solo. Sets like the Off-Road 4x4 Mountain Truck (60447) are rated 6+ but reviewers say motivated younger builders can manage them with a parent.