Stenroth’s father worked for the Finnish railways as the head of the Värtsilä station. Stenroth took his matriculation exams in the Nurmes mixed secondary school in 1915. Stenroth knew many languages. The Swedish language appears to have been his native language, in addition to which he naturally knew Finnish, as well as German and Russian. He started his studies in the Helsinki Business School, but they were cut short by the Finnish Civil War. In the war, he fought in the Helsinki Jaeger Brigade, e.g. in the Battle of Helsinki. Having participated in the war, he was now attracted to a military career, and he was accepted into the Artillery School in Lappeenranta. There he studied with e.g. future General Lieutenant A. F. Airo.