You should be measuring that population as a % of their total population. Not sure why you're comparing absolute numbers.
China has triple the young people we do, but quadruple the old people that depend on the young people.
China has triple the young people we do, but quadruple the old people that depend on the young people.
The other thing to look at in those population distributions, besides the upside-down age distribution, is the absolutely pathological gender imbalance. The number of surplus males under 30 should be keeping Xi Jinping up at night because if there is anything that is going to trigger another revolution it is tens of millions of disaffected young males migrating across the country who eventually get fed up with what they perceive as a dead-end future.