Immaterial. Improved agricultural knowledge will easily take care of that, as it has done so, before.
China has a far more serious ageing population problem due to its idiotic forced one-child policy. Soon, China will have more old people to take care of, than youngsters who will be paying an increasingly greater price to support them.
The issue is not the availability of improved agricultural methods but whether India will adopt them successfully. Indian farmers are predominantly small holders, this makes adoption of new methods / technology tricky. There are also problems with preservation - a good proportion of farm produce is lost due to inadequate storage / transportation.
India is also heavily skewed towards Services, Telecommunications and Pharmaceuticals. The Industrial sector employs only about 8 million people - these are not the numbers that will take many farmers off their small holdings and free land for optimised agricultural practices.
To change this will require aggressive policy adjustments and real political will. (I don’t envy Indian politicians!).
China can deal with its aging problem by eliminating the one child policy and implementing a guest worker problem. Nothing stops the Chinese from heavily recruiting workers from densely populated South East Asian nations like Indonesia and the Philippines. Secondly, China could simply place more emphasis on automation and increase worker productivity. (The technology already exists).