For India as a whole, I'd say several generations.

However, somewhere like Goa will get there much faster. A quick search turned up that Goa needs to roughly 4x it's prosperity to reach the low end of a modern western nation.

At 12% growth (not sure how feasible that is, but it doesn't seem insane), GDP doubles every 6 years and 4x is two doublings, so in 12 years Goa might be a recognizably modern economy.