On most airlines, a baby has to be more than one week old to fly. In general, you should get approval from your pediatrician before traveling internationally with a child less than six months old. Also remember that your baby needs their own passport.

There is no universal "youngest age" to fly, but most airlines have a minimum requirement of 7 to 14 days old. For example, American Airlines and Delta allow infants as young as 2 days old with a physician's letter, while others like Southwest require the baby to be at least 14 days old. Health professionals generally recommend waiting until a baby is at least 3 to 6 months old if possible, as their immune systems are still developing and the pressurized cabin air can be harsh on their ears and lungs. If you must fly with a newborn, it is critical to consult a pediatrician regarding the risk of infectious diseases in crowded terminals. Most airlines allow infants under two to fly as a "lap child" for free or at a reduced fare (usually 10% of the adult fare plus taxes on international flights). Always carry the child's birth certificate or passport, as gate agents frequently check for proof of age to ensure the infant meets both the minimum age to fly and the maximum age for lap-seat eligibility.