user21741: Are there any over-the-board tournaments open only to persons over 18?
Everywhere I go it's like a school field trip, more than half the players are from some elementary or middle school, all parents in tow. And as I am in the ~1600 rating range myself, I end up playing nothing but kids and I find it unpleasant.
First of all, it's a no-win situation. If you beat them, you feel like a bully taking candy from a baby.
Most of the time it's fine, but I've had a few very negative experiences, especially:

A kid about 9 years: he played a fantastic opening against me, he was
up a pawn and had a crushing position. He proceeds to go get all his
friends to look at the board, all snickering. Then, I fight back and
when he realizes I'm about to win his rook and take the initiative he
breaks out into tears, like inconsolable. It was horrible. The TD
awarded me the game as forfeit.
A kid about 14 years old: He plays really fast, and I go up a knight
and have a good attack going. It's a complex position but I'm easily
going to be able to finish it. He proceeds to get up, walk around for
20 minutes (game 60 time control), comes back, makes a move, then
gets up again, another 10 minutes, and on and on until he had a few
mins left and then he played to the end (I won easily.) It was
ridiculous. I complained to the TD but he said there's nothing he
could do.

So I can't play tournaments anymore, it's unpleasant. Are there any tournaments that are open to only adults?

user1816: If you find yourself in the UK, the Central London Chess Congress at Imperial College has an over-18's policy due to licensing restrictions on the venue. It is, not just for this reason, one of my favourite events on the chess calendar.

user12629: There aren't many, but there are some. Sometimes, oddly enough, it can help to find a largish scholastic event and see if there's a corresponding adult event at the same time. For example, Wisconsin holds the Wisconsin Junior Open every year. And, at the same time and location (but on a different floor), they also hold the Veteran's Tournament, which is only open to adults.

user17425: There are tournaments for 50+ years old.  This is great as you can avoid immature 30 year olds.  

user19877: There are definitely some, but they are, clearly, not the norm as most organizers want to get the most players they can, and thus, make the most money they can.
Here are a few links of places that have regular adult tournaments. Some of these tournaments have gone by, but if they did them before, they probably would do them again. There are surely more, but I am not going to try to track down every one of them.
Of course, and I am one now, there are also senior events for those over 50; so you have something to look forward to.
Starting a local club that does one game per week, and excluding kids, might also work for you.
I do feel your pain. I got whacked by the number one 8-year-old in the country a week ago. His behavior was totally fine, but kids are always so underrated.
Berkeley, California
Austin, Texas
New Jersey
Tucker, Georgia

21741: <p>Are there any over-the-board tournaments open only to persons over 18?</p>

<p>Everywhere I go it's like a school field trip, more than half the players are from some elementary or middle school, all parents in tow. And as I am in the ~1600 rating range myself, I end up playing nothing but kids and I find it unpleasant.</p>

<p>First of all, it's a no-win situation. If you beat them, you feel like a bully taking candy from a baby.</p>

<p>Most of the time it's fine, but I've had a few very negative experiences, especially:</p>

<ul>
<li><p>A kid about 9 years: he played a fantastic opening against me, he was
up a pawn and had a crushing position. He proceeds to go get all his
friends to look at the board, all snickering. Then, I fight back and
when he realizes I'm about to win his rook and take the initiative he
breaks out into tears, like inconsolable. It was horrible. The TD
awarded me the game as forfeit.</p></li>
<li><p>A kid about 14 years old: He plays really fast, and I go up a knight
and have a good attack going. It's a complex position but I'm easily
going to be able to finish it. He proceeds to get up, walk around for
20 minutes (game 60 time control), comes back, makes a move, then
gets up again, another 10 minutes, and on and on until he had a few
mins left and then he played to the end (I won easily.) It was
ridiculous. I complained to the TD but he said there's nothing he
could do.</p></li>
</ul>

<p>So I can't play tournaments anymore, it's unpleasant. Are there any tournaments that are open to only adults?</p>
 1816: <p>If you find yourself in the UK, the <a href="https://union.ic.ac.uk/rcc/chess/2020/03/central-london-chess-congress-at-imperial-college-may-2020/" rel="noreferrer">Central London Chess Congress</a> at Imperial College has an over-18's policy due to licensing restrictions on the venue. It is, not just for this reason, one of my favourite events on the chess calendar.</p>
 12629: <p>There aren't many, but there are some. Sometimes, oddly enough, it can help to find a largish <em>scholastic</em> event and see if there's a corresponding adult event at the same time. For example, Wisconsin holds the Wisconsin Junior Open every year. And, at the same time and location (but on a different floor), they also hold the Veteran's Tournament, which is only open to adults.</p>
 17425: <p>There are tournaments for <a href="https://en.chessbase.com/post/golden-age-of-us-chess-for-players-ages-50-and-older" rel="noreferrer">50+ years old</a>.  This is great as you can avoid immature 30 year olds.  </p>
 19877: <p>There are definitely some, but they are, clearly, not the norm as most organizers want to get the most players they can, and thus, make the most money they can.</p>

<p>Here are a few links of places that have regular adult tournaments. Some of these tournaments have gone by, but if they did them before, they probably would do them again. There are surely more, but I am not going to try to track down every one of them.</p>

<p>Of course, and I am one now, there are also senior events for those over 50; so you have something to look forward to.</p>

<p>Starting a local club that does one game per week, and excluding kids, might also work for you.</p>

<p>I do feel your pain. I got whacked by the number one 8-year-old in the country a week ago. His behavior was totally fine, but kids are always so underrated.</p>

<p><a href="http://www.berkeleychessschool.org/programs/adult-chess-tournaments/" rel="noreferrer">Berkeley, California</a></p>

<p><a href="https://www.austinchesstournaments.com/faq#RVI_adult" rel="noreferrer">Austin, Texas</a></p>

<p><a href="https://njscf.org/october-19-20-adult-only-fide-swiss/" rel="noreferrer">New Jersey</a></p>

<p><a href="http://www.georgiachess.org/event-2471084" rel="noreferrer">Tucker, Georgia</a></p>
