Please Answer Me (experts only)

I'm not an expert but if a player isn't IM strength by their teens, then it is extremely unlikely they will become a GM. In the history of of rated chess, there aren't any players that have started that late and have become a GM (at least I'm not aware of them).
There are some older players that started later in life, that became very strong players, but I believe all of those were before FIDE started rating games and awarding titles, and only a couple, or maybe a few, were close to GM strength.
There also isn't a lot of money in chess, except at the highest levels. Players can make a living off chess but that entirely depends on many factors and most people that make money do so with teaching or writing. Even then, most other fields would be more lucrative, if money is a driving concern.
Possibly of interest:
https://www.chess.com/article/view/can-anyone-be-an-im-or-gm
What It Takes to Become a Chess Master by Andrew Soltis
https://web.archive.org/web/20140708093409/http://www.chesscafe.com/text/review857.pdf
100 Chess Master Trade Secrets by Andrew Soltis
https://web.archive.org/web/20140708094523/http://www.chesscafe.com/text/review916.pdf
Reaching the Top?! by Peter Kurzdorfer
http://www.thechessmind.net/blog/2015/11/16/book-notice-kurzdorfers-reaching-the-top.html
http://www.jeremysilman.com/shop/pc/Reaching-the-Top-77p3905.htm
What It Takes to Become a Grandmaster by GM Andrew Soltis
https://www.chess.com/article/view/don-t-worry-about-your-rating
https://www.chess.com/article/view/am-i-too-old-for-chess

You can become a GM at age 21 no doubt about it! Don't listen to the negative people here.
I would say 10 hours a day of study chess ( everything not just tactics), 6 days a week, no alcohol and healthy lifestyle( lots of physical exercising), plenty of sleep, 10 years time you CAN become GM.

You can become a GM at age 21 no doubt about it! Don't listen to the negative people here.
I would say 10 hours a day of study chess ( everything not just tactics), 6 days a week, no alcohol and healthy lifestyle( lots of physical exercising), plenty of sleep, 10 years time you CAN become GM.
That's probably true, and if you actually keep it up consistently it might not even take 10 years. But who would do that? 10 hours a day of chess is no joke!