The outcome of ubiquitous digitalization will vary depending on number of orifices in your crotch. Number of orifices will be verified by medical commission when you reach adulthood. In case of Ukrainian men this ruling likely impacts only those non affluent, their rich kids seem to have a good time in EU and around the world.
That's the usual thing. You either cross the border before turning 18, or you have fathered three kids (surprisingly, they don't have to be from the same woman) or you have a special exception for special reasons and promise to be back.
Last time I checked, the story was something like -- you need to log into the system, make you personal details up to date so they can summon you for the best job in the world, but they don't actually summon anyone from abroad yet for obvious reasons.
I think many men will keep their paper passports with 10 year expiration date. And renew it every year "just in case".