You shouldn't let people drink that are underage.
Keith is drinking a beer on his porch after completing yard work with his 15 year old son John.
Keith wants to commend John for a job well done.
Keith offers John an ice cream from a local shop as a reward for working hard in the yard.
Keith offers John a beer as a 'thank you' for helping out with the yard work.
John and Keith get a ride to the ice cream shop and enjoy sundaes together.
John enjoys the beer and begins seeking it out through other people on a more regular basis, forming a harmful habit.