well i would expect around the 8 years mark but it realy depends on the country/culture (i live in England). when i vistited Morroco a few years back you would see a couple of three year olds hanging out on there own.
see link
see link
see links
Age 18 see links below
age 18 see links
See Link Below'Child Refusing To Visit Other Parent?'
age 21 see link
There is no automatic age that a child can choose which parent they want to live with in New Hampshire. The judge looks to see if the minor shows sufficient maturity to make the decision without being coerced by either parent.
The child cannot make that choice. A parent needs to file a challenge, during which a GAL will present the child's view to the judge. Or, arrangement for the child to speak to the judge in private. The judge determines the child maturity, and related factor, in a custody change. see links
Age 18 see link
Age 18 see link below
See link below. Child Support Laws - At What Age Does Child Support Stop?