I'm in my forties, so I guess I lost a great deal of my reaction speed due to age. Seeing some kid playing minecraft really frustrated me, because compared to that, my own play was about half speed.

So I wonder, is there anything that can be done to get a faster brain?

According to these links, there's nothing you can do:

https://tinyurl.com/bme69npg

https://www.psychcentral.com/news/2018/09/13/as-we-age-loss-of-brain-connections-slows-our-reaction-time#1

Training in martial arts helps a lot, but you still wouldn't be able to match the reaction time of a teenager.

Alternatively, try stealth or turn-based tactics games.

Well, the direction Minecraft has gone in combatwise sucks anyway, so I just play with the monsters turned off.

I treat Minecraft like a computer lego set. Something to breathe in and be zen about.

Turn off the Turbo button on your PC case.
Oh shit! PCs don't come with that anymore... I guess I'm turning old too :D

Caffeine. Lots of. Improves reaction time and writing/key hitting speed.

I would say just play normally. As you play you will pick up a lot of what you lost before. Some of it will be muscle memory, and some of it just gestures you will get faster at as you get more inclined for it.

Alternatively play games that are turn based like rouge-likes, FTL, ToME, ADOM, card games, etc... Technically Turbo slowed your computer down... not sped it up... Intended to give slower speed for games/programs to the proper speed otherwise they went too fast during one particular upgrading era...

A game shouldn't be about rushing through it just for the sake of rushing through it.
You should enjoy it at your own pace.

Why do you care if someone's faster? This isn't a competion. Play at whatever pace let's you enjoy your games to the fullest.

I heard some drugs help. Frowned upon, sure, but you really want to pwn those kids playing minecraft, don't you?

Only until you get up stomping your feet to rave music and throwing shapes.

Theres a reason the Germans lost the Battle of Britain ;D

Ah, indeed. The carrots.

Don't play games that have a fast-pace. Play role-playing games or something.

You lose reaction time with age, father time is undefeated. When that kid reaches your age, they will be the exact same as you.

I also don't see how playing Minecraft slower than someone else can ruin your enjoyment. It's not as though you're playing Street Fighter or Counterstrike professionally where reaction time is key. Just play how you play and enjoy the experience. No one is judging you on how fast or slow you are at the game.

No, not really, you just need to accept that from now on it's inexorable mental decline until you die.

Slow and steady, says the turtle.

You must understand that young gamers often use some kinds of cheats/cfg files/strategies etc.
So not only your reaction is important.
There are also many drugs that improve cerebral circulation. You can try one of them.