I have to agree with the military suggestion above
In my opinion this is a very unlikely scenario given the time period.
At this time (1920s-30s) many young Poles (boys and girls) joined the Polish scouting movement which was a very different type of organisation than scouting in other countries; it was much more akin to a paramilitary organisation similar to army cadet corps in UK.
When war broke out these Polish scouts invariably enlisted (volunteered) into military units proper and without hesitation; many that were under age gave false dates of birth to be able to join the fight for their country. In the countryside there were also the paramiltary Forrester battalions which also had junior
branches for young Poles to join these units mainly transformed into military units of the Polish underground resistance army or partisan groups composed of adults and teenagers.
I believe it would have been exceptional to want to avoid military service at this time.
You will undoubtedly have read about the later scouts heroic exploits during the Warsaw Rising? Poles were (are) probably one of the most patriotic nations on earth...it is in their DNA.
In my opinion if one was giving a younger false age it was more likely to have been to avoid a Nazi German dictate that was age-related such as deportation to forced labour. This age was from fourteen upwards.
This age restriction was in practice abandoned later in the war as German losses in battle mounted and German war industries needed more labour to continue production so very young children (from Poland and other German occupied countries of Eastern Europe and USSR) were also deported to the Reich as slave labourers. Young children's small fingers were very adept at assembling small munnitions and many were worked to death in German ammunition factories.