Looking at Chechnya, the Georgian-Ossettian-Russian war, and observing that the entirety of Eastern Europe lurched into camp West around that time period, you don't have to be Nostradamus to imagine that Russia's desire to keep as much of the Soviet empire with it as possible will manifest sooner or later.

Which has nothing to do with its demographics, and everything to do with its politics.

... Also, Ukraine is facing the exact same demographic stresses as Russia. Also, demographics don't matter as much as, broadly speaking, industrial capacity in modern wars. They aren't about throwing an entire generation of men into million-casualty-offensives over no-man's-land.

If you think Russia invaded Ukraine primarily because of "demographic issues" i.e. territorial expansion for resources, I have a bridge to sell you.