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.