Can a 11 year old take norfloxacin?

Yes, providing 11yo. Has infection resistant to or is allergic to other first-line antibiotics.11-y-o may already be undergoing pubertal changes which makes child physiologically adult. Magic 18-y-o restriction proviso comes from the fda for all drugs, unless there have been approved trials in chidren < 18 years. Most drug companies avoid expense & institutional drug reveiw boards risks of such trials.
See below. Fluoroquinolones including Norfloxacin are generally not recommended to children under 18. Exceptions are children with cystic fibrosis, complicated urinary tract infection with multidrug- resistant organism, chronic suppurative otitis media by pseudomonas or anthrax.