Why does it seem like the top grandmasters are all very young?


The growth of kids these days is unbelievably rapid, so much so that their skills can already be elite at such a young age. However, it is said that after your peak (perhaps around 30 years old), you start becoming less sharp tactically, and as with anything else, cognitive ability declines with age.

Yea I think underdog is right. As someone who is 38 it's sad but true, you aren't quite as fast and sharp as you get older. Its obviously less of an issue than in more physical games like football or whatever, you can still get very strong players in their 60's and beyond, but I think to be at the very top of the game you need everything in your favour: natural ability, devoted training, and physical health and optimal mental speed
My opinion is that the optimal game strategy changes over time, and depends on how other players are playing. As the game evolves, experienced players must learn new strategies but may be more cemented in their ways than a younger player more actively looking to learn coupled with a more fluid learning ability as a result of young age.

If chess were about knowledge, then yes, the best players would be very old, but it's also about performance. It takes a lot of stamina to think hard for 5-6 hours (a single top level game) and do that day after day. It's not even enough to be young, because the young players also stay in shape. Carlsen and Caruana are in very good shape for example.

I think this doesn't apply to blitz chess, at least in my experience. I'm turning 65 soon and I've maintained a good rating on this website, at least for someone of my age.
I'm calling BS.
@1
"I would expect them to be much older in the 60s-70s because they have more time to learn."
++ Chess is more physical than you think: to maintain high concentration for hours is exhausting. That is why Kasparov, Kramnik have retired.

As we age, all of our physical functions gradually slow down. This includes the speed at which impulses travel through the neural system. This gives the younger person a slight edge in the amount of calculation they can do.
For a good part of our life this slowing can be offset by the greater accumulation of knowledge and practical experience. This very accumulation eventually leads to another problem--memories (of past games and what we have studied) are stored in the brain as a linkage through a series of neurons. As we accumulate more and more memories, these neural paths are partly overlaid by other memories, often letting our "train of thought" go off the track or switch to the wrong route.
So it is in the middle of our life that most people's mental faculties are at their best. Add in the physical rigors of a high-tension tournament or match and it is the earlier part of this time span that most people prouce their peak performance.