This coming Saturday I'd like to try to solve some CTF challenges, just for training. I'm a beginner, and I'm looking for people to try it out together - it's more fun and together we can do more.

There are many CTF training resources available on the Internet: http://captf.com/practice-ctf/. 
In particular, this one is good: https://picoctf.com/ 
And this: https://www.root-me.org 

If you are interested, feel free to join, I'll be at the hackerspace from 14h until 19h!