India Dispatch: The strongest case for India is not merely that it is young, but that it still has time, and it may be the only continental-scale economy that still has it in abundance. India won't cross the demographic threshold for an "old" country -- a median age of 41 -- until the late 2050s, while China reaches that point now. India requires 10.4% sustained GDP growth over 35 years to become rich before aging, compared to China's needed 32% annual growth rate. India's working-age populatio…