You can't make definitive statements like that. How much a government spends on a particular category is dependent on politics. Nothing is stopping the govt to spend less on elder care if they want to. The elderly will just depend more on their own savings or their children.But this does not resolve the dilemma between spending more on guns versus butter after 2035. China's aging population issues will force the government to spend more on universal eldercare. And that means less resources for the PLA (except veterans and MOD retirees).
China spends the least amount on the military right now. Less 1.2% of GDP officially. Technically China is the one that is following the pacifist constitution rather than Japan.
China spends the most on infrastracture, poverty reduction, education and so on. It spends on things that will boost China's economic potential, which in turn leads to higher GDP growth.
As China gets richer, its geopolitical ambitions will rise which means it will spend more on the military, not less. Right now, its in keep your head down, hide and bide, just focus on economy mode. As it gets richer, there is less incentive to keep silent. There will be more ambition to push for more influence and more power.