CPSC Guidelines for Age-Related Activities
Summary: Guidelines for ages when children are ready to use wheeled toys and vehicles from the US
Consumer Product Safety Commission
The best guidelines we have seen were on the CPSC site:
Age
Determination Guidelines: Relating Children's Ages To Toy Characteristics and Play Behavior
Note that an individual child's development rate may be very different from average expectations. CPSC updated the
guidelines in 2020.