Am I loosing time?

I don't know, why are you?

After years of playing and some study, I've achieved the ability to beat very weak players.  

I've wasted my life. : (

Does everyone on this site think they're gonna become the next Gary Kasparov? 

There's also this strange concept called playing for fun. 

errr, maybe because it's fun? you have to answer that question for yourself lol. if you can't come up with a reason, it's probably a good time to stop playing.

If you like watching movies and also think watching movies is a waste of time... then you've got to stop watching movies and find somehting else to do.  Same with chess.

Tax is funny.  I hate it until I find friends paying more than me; then I hate low income.  I want to earn less so I pay less tax, but I want to earn more so I can have the things I want.  I like to play chess because it is fun but I hate playing because it wastes time. It is a tough time we live in.

"why am I still playing knowing that I will never achieve anything concretely?"

This is too vague. What's exactly your goal? To be a professional? Well, depending on your age, it may be possible or not. Your goal is to increase your daily/blitz rating in 300 points? Totally doable.

I don't like sugar coated advices. If your chess standards are way too high, then it's better to quit, simple as that. I mean, you only live once, so it's better to spend your time with things that you actually enjoy.

The notion of a player "hitting their peak" is absurd.  It happens mainly because the player himself (or herself) accepts that they can't get any better.

The issue is that the methods of getting from one level of play to the next change as you improve.  At a certain point, the next step is not as obvious as the last, especially if you don't have better opponents to work against.  Periods of stagnation can last a long time (I've had a lengthy one myself), but eventually a better understanding of the game (or at least certain aspects of it) will become apparent if you play often enough, and challenge yourself by playing tougher opponents.

Nothing is more satisfying than that first victory against a player who is at that next step.  The first time I beat an Expert was thrilling.  For the first time in a long time, I realized that my improvement as a player was ongoing, and that I was a much better player than I was only a year or two earlier.

The great thing about chess is that there's always another level to seek.  How many hobbies are there which offer such a constant challenge as that? 

^ I think this is biased. Most hobbies are this way...

Every game you play is different, so every game adds just al little to your experience. But after a 1000 games, a single game only adds 1/1000 of the experience of your first game. Maybe you will never be the best of the best, but by every single game you play, you will be just a little bit better than before. Personally, I play for the fun of it. Only you will know, what your personal drive is.

". In addition chess theory is huge, everything has been already discovered"

Unless your goal is to have a chess opening named after you - why would you care who discovers some new move in opening theory ?

BTW,  many once-popular opening novelties get subsequently refuted.

Even if you never "achieve" anything "concrete" (like a chess title, or tournament win), you can still "achieve" an ability of being a strong chess player. Even if chess is played without the "fun" (which would be sad, as chess should be "fun"), you can still achieve a lot; you can get the satisfaction of attaining a strong ability towards something you constantly work at. This forum actually has less to do with chess, and has more to do with: "why do we work towards any goals, or care about anything?" This is more about motivation and time management, than about anything else. View chess as a hobby, or a personal goal; if this is not true for you, then perhaps you should consider quiting chess - and taking up something else that feels like time better spent. However, if you are like most of us in this forum, then you will stay with chess - and continue to partake in the world of chess as well as the chess.com community.

Yes, chess is a huge waste of time. . You only enjoy 50% of the time which is when you win, and most people never reach GM. It just depends on how much of your life you want to waste rather than doing something useful.