I'm 14 and I started playing chess from 7 or 8 years ago, but now, I didn't think about being a grandmaster. So what should I do? Should I quit?
If you're 14 and not a grandmaster yet, it only means that you probably will not become a contender for the world chess championship. But most lesser goals should be achievable, and "only" wishing to become a grandmaster is definitely not out of reach for someone your age.
What it all boils down to is whether you're determined enough to put in the work that is required to become a grandmaster at chess. Are you prepared to play much, and make systematic study of chess a part of your daily life? Depending on your talent and other circumstances in your life it may or may not be difficult to reach your goals, but it's unwise to assume it will be a breeze. Assume that you will have to work hard for a relatively long time, otherwise you will only become disappointed.
So, trying to become a grandmaster is a big committment if you're not already close to achieving the title, and therefore I think it would be wise if you tried to figure out why it is so important for you to become one? Why on earth would you need to stop playing chess just because you couldn't become a grandmaster? The overwhelming majority of chess players in the world aren't even close to that level of play, and most of us don't even care! I believe that most people play chess because they think it's fun, and not because they want to become a grandmaster.
Maybe the above paragraph is misguided, and you simply wonder whether you should quit trying to become a grandmaster, and not whether you should quit chess altogheter. In that case, please ignore it.
You need a few things to become a gm.
1) A commitment to improving and a never give up attitude. For example if you trained 5 hours a day for 5 months straight, then played in a tournament and had your rating go down 50 points that couldn't phase you. You would just have to trust in hard work, continue your training and then 2 months later you'd suddenly win a tournament and gain 100 points.
2) A good training plan. There are certain phases of the game and you'd need to make sure you were training at each phase in the correct order, with the best training materials possible, and you'd need to be very focused during the training. You'd also need a good eye for your own weaknesses and come up with methods to overcome them. If you trained blitz tactics 2 hours a day and found in tournaments you were moving too fast and not calculating deeply enough, you may start studying tactics without any time limit attached, and only move when you think you truly see the answer and you have fully explored the position.
3) Stamina. Playing 7 6-hour high pressure chess games over three days can be grueling. Getting inshape, eating healthy, exercising between rounds, and getting 7-9 hours of sleep everyday can help insure you're going strong by the time round 6 and 7 roll around.
4) Get some feedback from strong players on your games. Whether the local chess clubs top player is willing to help mentor you, or you find yourself a coach, it helps to have someone else looking at your games and having them find weaknesses you can improve at.
For general study I'd suggest always training tactics 1 hour everyday, reviewing a master game a day, reading a book on chess strategy everyday, reading an hour of an endgame book each day, and playing and reviewing a long classical game each day.
If you are ready to commit to becoming a top player and are pumped up to be a master yourself following a tough training schedule, I think you have a bright future in chess.
The masters who don't become gms generally quit training and don't believe they can do it. You have to believe, go for it, never give up and train hard for it to have a chance at gm.
https://en.wikipedia.org/wiki/Maurice_Ashley besides the fact that he is the first black GM he also became IM at the age of 27 and GM at the age of 34. So it is absolutely achievable.
It's not easy though. But you still have lot of time, there are people who become GM's in the middle of their 30's (they don't start then of course, the point is you can still develop at that age).
Yasser Seirawan didn't pick up a chess piece until he was 12. He reached the Candidates Matches twice.
He was World Junior Champion at 19 and for a decade was America's best hope to break the Soviet monopoly on the world championship. In fact - he did something that Fischer didn't accomplish until his last sanctioned match. He defeated a reigning world champion over the board. (Fischer had never beaten Spassky or his predecessors until his famous match.)
My best advice to you: read every book by Yasser Seirawan, and watch every one of his videos. Maybe it is because he learned the game at such a late age that he is indisputably among the greatest teachers of chess of all time.