Whats wrong in joining the Israel Army in a Nachal Chareidi unit if the boy can’t learn Torah full time and wants to go to work after his Army service?
On the contrary, it is a Tora obligation (Rambam Hilchot Melachim 5:1 and 7:4)and it is forbidden for them to think of their families or personal safety (ibid 7:15). Deserters’ forelegs can be cut off by people who are tough and aggressive (ibid Halacha 4).