when do we reach our ceiling?

I started playing chess as a kid, and stopped in my teens (no surprises there). After a 35 year break I started playing online about 5 years ago, initially with the computer and then against "real" people.

I seemed to peak in mid 2021 in the mid 1400s and am now about 100 lower rated.

I'm sure that there are exceptions who study for hours a day, but for ordinary mortals when can we expect to stop improving?

No one really knows.   

Have you studied a lot?  It doesn't look like you've taken any of the lessons here.

And it looks like you stopped playing for most of this year, so if your rating fell off a 100 points or so, it isn't surprising.

There's no reason to give up.  A peak rating is interesting but you can still have many stimulating battles even if you aren't climbing the rating ladder.

You stop improving when you stop learning from your mistakes.

For many, this means playing games without analyzing or reviewing afterward. Doing so will rob you of the opportunity to learn and grow as a player.

If you review all your games after playing them, and actively try to learn something from each game, you'll inevitably get stronger over time ...

You reach your ceiling when you climb your ladder (or stepladder, if you're tall enough).

exactly

My answer is similar to @ironsteam1 but I'd add that the tricky part is that working on chess and learning from mistakes means different things to different people.

For example, for me, looking at my online game briefly with an engine after it's over, is fun... when it's fun a person can do this over and over for years with no trouble. For a different person that activity may be "work" and so they stop after 1 month, or 1 year, or 10 years, but they eventually stop. For me, it's too much work to study a book, so I don't, but some people have read over 100 chess books... some people have read this much in only a few years.

So my answer is you stop improving once you stop learning and stop changing the way you play... but there's no "mere mortal" level for that, it's a different level for every person, and it mostly depends on what you consider fun.

There are people who play hundreds of thousands of games but don't improve much. For example this guy has played almost 400,000 bullet games and is rated under 1000.
https://www.chess.com/member/peacemyfriend
So a person stops improving when improvement activities aren't fun to them.

 

But the sky has no ceiling.

Everyone has a ceiling.

'He evidently has an extraordinary good memory, for he always makes the same mistakes'
- Steinitz

Key is to analyse your lost games and learn from your mistakes.
As long as you do that, you make progress.
Otherwise it is normal to be slower and weaker after a longer break.

@10

Yes, after reaching the ceiling comes the downhill road. Age gets the better of us all.

note that rating is very uncertain

 

Do we know what exactly becomes harder when we age?

It is not uncommon for chess players to experience ups and downs in their ratings over time, and it is not uncommon for players to have a peak rating and then see their rating decline slightly afterwards. There are many factors that can influence a person's chess rating, including their level of practice and study, their physical and mental health, and the quality and strength of their opponents.

As for when a person can expect to stop improving, it is difficult to say, as this will vary from person to person. Some chess players continue to improve and progress throughout their lives, while others may reach a plateau or decline in their ratings at some point.

There are a few things that you can do to continue improving your chess skills, regardless of your age or current rating. These include:

Practicing regularly: Consistent practice is one of the most important factors in improving your chess skills. Try to set aside time each week to play games or solve puzzles, and try to mix up your practice by playing against different types of opponents and in different time controls.
Studying chess: There are many resources available for studying chess, including books, videos, and online tutorials. By studying chess, you can learn new ideas and concepts, and get a deeper understanding of the game.
Analyzing your games: After each game, take some time to analyze what you did well and what you could have done better. This can help you identify areas for improvement and help you develop a more strategic and effective approach to the game.
Seeking guidance from a coach or mentor: If you are serious about improving your chess skills, you may want to consider working with a coach or mentor. A coach or mentor can provide you with personalized feedback and guidance, and help you develop a plan for improving your chess skills.
Ultimately, the key to continuing to improve at chess is to stay motivated and committed to learning and improving. By setting goals for yourself and working towards them consistently, you can continue to make progress and improve your chess skills.