Not sure how you came up with this number 70? If you meant starting as a democracy gives the country a head start, it doesn't. Political system hardly matters as long as it doesn't suppress people's freedom, the intent to start working on policy changes to create eco system for business activity to thrive gives that start and India started that only in 1991. You may ask why it took 45 years to get started with economic reforms. 200 years of British rule which began with "East India Company" starting business in India and then expanding its business in to providing mercenaries for local Kings (yes you are seeing Wagner group now, but India saw all this from East India company 300 years back) and ultimately establishing its own rule on the whole country left a deep psychological trauma not only on Nehru's psyche but on all Indians. So when he came to power Nehru started viewing any big Corporates with suspicion and created a state owned enterprise model which was largely in-efficient). Now i fail to understand why it took 30 years for China to start doing the right things after CCP came to power. It never suffered from free trade did it? Silk route always gave it good trade and development.
Yes, the 70-years head start by India is because India was never a communist country and China still is. India has the same headstart on China as Taiwan and South Korea have.
Every country with the democracy that India has -- UK, France, US, Germany, etc. -- are far, far, far wealthier than every commie-run state.
West Germany was FAR wealthier than East Germany. South Korea is FAR richer than North Korea. And Taiwan is FAR richer than China. The only difference is those places of the same people, culture and location is communism. There is no doubt about this.
The penalty that Communism imposed on China and is still imposing on China is far greater than whatever arbitrary years India thinks China has started. What allowed China to offset communism to an extent is following the East Asian Model. But Communism still made China only a third as wealthy as the other East Asians.
Again, the difference between China and Taiwan is Communism. The difference between India and Taiwan is the East Asian Model. The difference between India and China is the East Asian Model plus the detrimental effects of Communism on China.
All I'm saying is India cannot use China's past to project India's future. China is communist and East Asian while India is neither. There is no shared factors here to make China a more likely model. Chances are India can follow Nigeria's past 15 years or Germany's past 15 years as likely as China's.