How many years behind is not a very meaningful statement, let's guess how big India will grow in the future. Optimistically estimating that India will maintain a growth rate of 6.5% in the next 20 years and 3% in the following 20 years, India can grow to 6.3 times its current size in 40 years. This scale is enormous and can support India to become the world's third largest military power and second largest industrial country. Based on India's military spending ratio, it is estimated that India's military strength in 2065 will significantly surpass that of China today.
After having sufficient military budget, India will also imitate and develop, just like the People's Liberation Army. Currently, India still imitates outdated fighter jets, ballistic missiles, air-to-air missiles, and drones. With sufficient industrial scale in the future, India can also develop large warships, strategic bombers, sixth generation fighter jets, and so on.