If the answer above is None it means there is no specific mention in the legislation, but you still need to ask local law enforcement before drinking in Chad.
Law 2017-01 Penal Code Chapter 6 Articles 376-378 establish penalties for licensees who permit entry to youth below age 16 unaccompanied by a supervising adult, sell or offer alcohol beverages to youth below age 18 unaccompanied by a supervising adult, or serve a person below age 18 to intoxication.
You can find more legal details and links here:
Wikipedia Legal Drinking Page