As someone who was serially consumed by various philosophers when I was younger, I totally disagree.

Going all in on a philosopher at least once, especially when you're young, is the best way to really appreciate philosophy. It's the difference between understanding what the philosopher thought and understanding what it's like to truly think those thoughts and be immersed in the value system.

I have read philosophy before turning 25 and hence, and I both agree and disagree with this advice. On the one hand, I’ve certainly had my fair share of realizations of how daft I was when I read the works when I was younger and how quick I was to adopt the ideas of others without really understanding them. On the other hand, I wouldn’t be able to contend with a vast number of texts that I do now without the background and terminology I absorbed by being a bit arrogant and tackling some of the works that I had when I was younger.

In general, you can bolster your defenses against unwitting influence if you have a good teacher guiding you and reminding you to be critical. This is more or less the point of dialectic.

Your last advice is critical, but I've seen people fall into voids and make twitch decisions and statements about important things in their lives with consequences spanning years, because they have a philosopher's aura around their fledgling heads. Besides, we can still be plenty arrogant at 25, 30 and 40 but with a bit more consistency.

Out of curiosity, what would a nihilist with a cause look like?

I know, I know, but a cause could be just sustained senseless but concrete suffering, as opposed to imagined sorrow.