The series revolves around the adventures of the title character , Johnny Test , an 11-year-old suburban boy who lives with his super-genius 13-year-old twin sisters , Susan and Mary , both of whom are scientists .
The series revolves around the adventures of the title character , Johnny Test . He is an 11 to 13-year-old suburban boy who lives with his super-genius 13 to 15-year-old twin sisters , Susan and Mary , both of whom are scientists .