While Latvian population pyramids are not as upside down as Russian ones are
They both show a very similar dramatic decline in births in the last 20 years. Both the percentage of children and the percentage of Russians have trended steadily downward in the past 2 decades.
If Putin wants new young Russians, maybe a constant loop of Barry White songs would be more effective than invading the Baltics.
edit
This does put the Latvians in more serious trouble in 15 years when they only have 60% of their current Military age men available. The Russians will have similar demographic problems, but as they have a larger population in general it would probably be easier for them to shift people around.
sources
http://en.wikipedia.org/wiki/Demographics_of_Latvia
http://www.indexmundi.com/latvia/age_structure.html