Do you think China and Russia just let these military aged men leave?
I don’t know about China but in Russia, unless a man is in the military or has an active mobilization order he can leave Russia at any time, for any reason, without question (as long as he has a valid passport). For that matter any Russian citizen can return without question either (this came up during Covid where many countries weren’t even letting their nationals return). Russians are pretty sensitive about this and made sure it was very explicitly expressed in the Constitution (after everything that went on in the USSR with exit control).
The military aged men were sent , like the Chinese dictator has many police stations in democrat controlled cities. buying land next to American military bases, and more = Invasion
China - people leaving the country for any reason have to have CCP approval.