Excuse wall of text. TLDR Generic demographic doomer math based on naive reading of demo pyramid fails in PRC case (and many others), demographics =/= destiny, i.e. doesn't account PRC social economic factors. Not all cohorts are equal in income/education disparate country like PRC, where old cohorts are literally worth "less", which allows PRC to arbitrage between young/educational/rich vs old/uneducated/poor.
1) Workforce is 20-60yos, conservatively ~600m (more with retirement reforms) in 2045, roughly 2-3x US workforce with disproportionate STEM bias. If current tertiary trend keeps up, that's 6-8x US STEM workforce backed by RoW combined in automation synergy, which will slowly decline over decades, and since white collar they can hang around much longer past retirement unlike blue collar. Now the 2045 demo pyramid is not favourable for 2065 talent generation and if no fix, trend towards disastrous by 2080s, but in terms of actual absolute high skill workforce advantage vs competitors, it's almost unassimilable amount combined with industrial density for like 50 years. That's within the timeframe of building hegemons.
2) For 2045s 65-85s - they are overwhelmingly old/poor (undereducated, left behind by modernisation). They "weigh" SUBSTANTILLY economically less than their actual headcount. The bottom 2 quantiles of PRC constitutes Finally flip side of 4:2:1 ratio, where the 4:2 has high savings + property) is once older generation starts to croak = multiple wealth transfers to younger gen (at least in terms of property). If extrapolated (this is speculative but mechanically likely) much of current PRC TFR issues is combination of excess competition and delayed family formation due to absolutely brrting tertiary in compressed period where talent:job supply:demand are mismatched. Current cohorts are growing up in fucked period where 20m new grads were competing for 15m jobs, vs near future where 10m new grads are pick and choosing from 15m+ jobs. By 2030s, aka when most current skilled cohorts are established it's going to be MUCH easier justify having kids, because projected involution pressure will be gone, no need to be top 1% of gaokao etc, unless AGI and crazy automation because their kids will be guaranteed to enter society with stupid amount of job vacancies / opportunities, and likely multiple properties. Like the natural outcome of current demo structure is most PRC new gen will have roof over head, not live paycheck to paycheck, and once cost of competitive child rearing goes, because every child guaranteed job, all current factors stalling family formation disappears. Of course other factors can throw this off, but this is likely where current PRC demo + social economic factors will converge.