I'm from India and I just recently quit to start on my own. I'm 33 - I got my GC 1 year ago.
My sincere advice: Stay in India.
India is going to hit the point where everyone starts doing things on the internet. Its very nearly there. But when it explodes, there will be tons of of money to be made. You will be sitting on huge numbers of people just learning to use the internet for their daily lives.
And I would definitely advise you to join the startup. You will learn nothing but tech from Amazon. I would even take a paycut if you can ask for some non-tech responsibility in the startup, ie on the business side. You need to understand how the deals are made - even more so because your dealing in India.
Stay in India and learn how to start your own business - catch the upcoming internet wave. You are positioned perfectly to ride this out and make millions. I'm serious about this.