Under Parliamentary law, military service began when a man reached the age of 21. After three years of active service, men were transferred to the "Reserve," where they could be recalled until reaching 33 years of age.
Active duty, after 1890 was 24 months. A male reaching age 21 could be called during any two-year period and at any time of the year. After those 2 years of active then they would serve the balance of their time as reservists and would participate in the autumn maneuvers of every second year if they were needed.
Of course some did not serve if they could not meet minimum requirements.. one of which was minimum height of 5' 2" (1.530 meters)
1) A person "may" have gotten an exemption for:
The son, or son-in-law of a father who was unable to support himself, or who was a widower.
2) An only grandson, if he was supporting grandparents who were unable to support themselves.
3) The employed brother of orphaned minors.
4) Too short under 5’2” tall
Also special reduced active duty was given to college students if they joined while in school.
Of course war time changed things and it appears the men younger than the above mentioned age of conscription served during WW I.
Croatian Heritage Museum