How old is a child usually when he's lost all baby teeth?

Varies. Some children begin to lose baby teeth as early as five and others don't start til seven...Usually by middle school (10-12 years) most children have lost all their baby teeth.
Varies. On average girls have lost all their 20 baby teeth before age 12, boys a year later. This can vary 2 years on either side of the norm, however. Pediatric Dentists & Orthodontists have the greatest depth of growth & development training. Please DO NOT wait for all baby teeth to be lost before seeking an Orthodontic Consultation.
Losing baby teeth. A child gets his first permanent teeth at age 6-7 years of age, and gets his last adult teeth (except for wisdom teeth) at age 12. Usually the last baby tooth is lost at age 11-12.