Stanford's Center on Longevity provides some intriguing long-range projections for working age (16-64 year) populations in Asia through the year 2050. As the chart below indicates, the most profound "worker bulges" occur in countries of South Asia--specifically India, Pakistan, Bangladesh--as well as the Phillipines. India's employment segment expansion alone is near 300 million people.
Important to note is that these are all of these countries in dire need of significant upgrades to overall education attainment and skills investment. The clock is ticking.
As a corollary, both Vietnam and the US will also have relatively young working populations by mid-century, whilst China, with an 18-year old population that peaked around 2012, is expected to have a workforce declining relative to 2010 (but still approaching 900 million people).