Long, shining, beautiful and black hair is the dream of every girl, but unfortunately, everyone is not blessed. What should a girl do to get heavy mass of silky and sweet mane, on the head?

I eagerly want the answer.
Also, please tell, if someone can, how can one procrastinate the 'whitening' of hair, which happens with age, in Asian countries, esp. India.

Hair growth and thickness is all genetics. There really is no magical lotion or pill that will make it grow faster. The average hair growth rate is between 1/4 and 1/2 an inch per month.

Eating a healthy diet, can aid in having healthy hair, here is a link to a site with some great diet tips:
Top 10 Foods for Healthy Hair

Split ends and hair breakage can make it appear as though hair is growing slower as well as make it look dull. Avoid using blow dryers and curling or straightening irons as they damage the hair.

There is no way to stop your hair whitening or greying, another thing often caused by genetics. If your parents went grey early you have a higher chance of it happening to you.
There are many hair dyes that cover up grey, both permanent and temporary.

But, I have heard many people say that their hair has started getting grey due to malnutrition or some ailment. My brother is in IAF - Indian Air Force - as a medico, and he has to move throughout India, and has to consume every type of food and water and experience every atmosphere, which has greyed his hair, much even as health-wise, he is awesome. Many people claim that hair greying can be delayed by certain methods, but I do not know whether to believe them or not, but your saying that hair can be permanently blackened is something of a cheerful news.

Please tell if there are certain foods or drugs, which can help, even a bit, and also I want to tell that straightening is necessary to make hair look good.

If you must straighten your hair make sure you use an iron with ceramic plates, not metal ones. Any large amount of heat is damaging but the ceramic is less so.

If you and your brother are under 30-35 and you think the greying is not genetic then you are right it may be something else. I had to do a bit of research into greying hair as I admit it is not something I know a lot about, I know more about hair care so I appologize for giving you links for this next part.
The Science Of Grey Hair
This site gives some information about the science of grey hair as well as attributes smoking and illness.

What Causes You To Have Gray Hair At A Young Age? | LIVESTRONG.COM
Lack of sebum is labelled as a culprit on this site, it can be caused b vitamin deficiencies.

It would be best to check with a doctor before putting any added vitamins into your diet. You may be lacking in a certain vitamin but there may be a medical reason behind it which of course, you would want to find out why rather than just taking extra.

Is it true that cutting the hair helps in speedy growth, where as it is also often heard that if one removes the grey hair by plucking, their number enhances. Also is it said that shave (head shave even) helps to enhance or accelerate hair growth.

What is the truth?

For long, silky, thick hair, one thing you can do is go on a certain diet. Some things you can eat are salmon, walnuts, eggs, sweet potatoes, and spinach. I'm sure there are more foods. Also, you can massage your scalp regularly and that helps a lot more than you would think. Trimming also helps because split ends prevent hair from growing faster. Hope this could help!