Its up to his parents but i don’t believe a child under the age of 18 is wise enough to make a rational choice about his future. It may be unwise to close his opitions.
Still your right as a matter of policy a child who gets held back too many times might be suggested to drop out to look at alternatives be it a different kind of school or ditch digging.
In either event i feel the state and local government owes the child a refund on his remaining amount schooling that he will be paying taxes for for the rest of his life. It would of course be extremely unwise to give this to them before 18 unless its in the form of a voucher for an alternative education institution.
Well somebody has to learn so they can give him a job.