As detailed on Formationsgeschichte – Rekrutierung (agw14-18.de), the drafting system in the German empire was fairly complex.
According to this site there was a conscription of 2 years for most branches of service, starting at the age of 20. The draftee was part of the reserve for 7 years (2 years conscription + another 5 years), then he became part of the Landwehrpflicht.
I want to narrow down the birth year of someone who was fighting in 1915 in an infantry reserve unit (Reserve-Infanterie-Regiment Nr. 227) as a Gefreiter (= Lance Corporal).
Can I safely assume that this person completed his conscription before the war broke out in 1914 and was as a part of the reserve at least 22 years old, thus being born 1892 or earlier? Can I draw any assumptions on his age from his rank in 1915?
Thank you for sharing your experience.