The conscription web page mentions the following:
What is this "another check-up" and how often is it organized? Until what age is newly become citizen one liable for conscription? I read somewhere its 30, is that right? Am I liable for army service if I get citizenhip couple of months before I turn 30?A person liable for military service is not a conscript, who has received Finnish citizenship or decision on citizenship in the year when they turn 18 or after that year. They can, however, be ordered to another check-up organised by the Regional Office.
Thansk!