1. Yes it takes months to drop corona virus cases down due to it's lifecycle of many weeks and 80% in 4-5 months is a massive drop.
Please stop pulling the other one about India being more disciplined than countries in Western Europe where cases over autumn and winter have shot through the roof. In UK mask wearing is a legal requirement and hand sanitiser is available everywhere free to use.
2. Please try to understand that warm weather inhibits the virus to some extent but obviously if people pay no attention then it will still spread. I cannot make it any simpler than that.
3. No they are not if they are not overweight or have co-morbidities.
A healthy 55 year old maybe has a 1 in 10,000 chance or lower chance of dying, and this is from the probably more unhealthy UK population covid-19 deaths data due to more unhealthy lifestyles in the West.
Wow, 300 million Indians are vulnerable? Only 2 million people in UK have co-morbidities that makes them "extremely clinically vulnerable". Say India is similar then that would be 40 million or so Indians.
So many sick Indians according to your information. Indians must be far more sicker than BD'shis, Pakistanis and Africans then. Indians are officially the sickest nation on earth by a mile according to your own government.