Kids under 2 years old can travel as an infant with their parent's lap. Moreover, children 2 to 12 years old are considered minors, but the age limit for traveling alone on airlines is 5 to 12 years old, and it is the ability to fly alone. To learn more about flight age limit, visit the Airlinesunaccompaniedminor website.
https://www.airlinesunaccompaniedminor.com/blog/what-is-the-youngest-age-to-fly-alone