You forgot, civil service also counted. But the time before you got your franchise was longer.
But yeah, just a few changes are needed.
I now actually read the book again, and I guess what you mean is that they could also attain the right to vote by serving in a non-combat branch / role of the military.
What struck me as the most important point in the book was something the teacher said while Rico was being trained as an officer.
"What is the difference between voters in our system, and those of the systems that came before and failed?" "I will tell you" "In our system, every voter and every person holding public office has proven through his voluntary and difficult service that he values the welfare of a group more than his own personal gain"
toghether with "Authority and Responsibility must always be equally large, the unlimited democracies were unstable because their citizens could exercise their sovereign authority without bearing responsibility for their actions. "
(I am paraphrasing since I don't have the English version of the book.)
What's important to note though, is that soldiers where allowed to vote only After they finished their service, not while they where still a soldier.
Now the military component of such a society would only work if there is actually a formidable enemy to fight. Personally I would like to live in a society where everyone is required to complete a period of community service before he / she is awarded the full benefits of citizenship, with required regular repeats. Elected officials would have to serve more difficult terms because of their increased authority / power.
I also noted again what an awesome piece of military propaganda the book it, every time I read it I thought "daaaamn, now I want to go join the Mobile Infantry to kick some ass!"