It could explain why Putin was forced to make a military move now. In another 10 years, Russian will be unable to field troops unless they want to send a bunch of 40 year olds into combat.
That's what some people who've looked at the demographics say. But Russia's real manpower problem is the lack of well-trained reservists and the lack of a proper mobilization system as a whole. There are 14.3 million men aged 20-35 in Russia. That's more than enough to field an army of 1-2 million men, which should be sufficient for any task.
The problem is that about a decade ago, the general mobilization system inherited from the Soviet Union was dismantled. That explains the chaotic manner in which the current "partial mobilization" has proceeded. A mass mobilization system also depends on adequate numbers of qualified trainers and training facilities as well as materiel and equipment in working condition or able to be refurbished quickly enough to field as part of a mobilization process. It does not help if fielding the equipment requires industrial rebuilding. Corruption has hollowed out the existing preparedness to an extent foreign military experts or even Russian leaders were unaware of.
What we're looking at is Russia throwing poorly prepared reservists and convicts (in the ranks of the Wagner Group, a PMC) into the meat grinder while a proportion are receiving better training (or maybe not) in Russia or Belarus.
By the way, Russia is already sending men aged 40-50 into combat. Some of them have scarcely any training let alone fresh training. They've even been sending alcoholics and chronically ill people into training centers for quick training and then into combat. This explains the huge numbers of KIA they've had in the last three months. Many of the wounded who would've been successfully treated in the field and evacuated into safety in any Western military have bled to death due to the poor field medical supplies and training. Reportedly, at least 700 000 men have left the country after the "special military operation" began last February.