I have been playing RPGs on and off for almost 30 years. Mostly with the same people. More often than not I am the DM/GM/Storyteller. The number one thing I noticed that changed with my friends roleplaying in their thirties versus roleplaying as teens and young adults is that they roll with the punches when their character fails at something rather than try metagame out it. Yes, if you rolled poorly on a perception check in a dangerous place and your DM is checking his notes, you know something is up. My sixteen year old friends would try to justify a defensive measure. My 36 year old friends just okay "alright, room is safe, I'm going to relax." Same thing if a character rolls badly at a sense motive check. "Yup, this guy is trustworthy." Or if the character botches a lore roll and thinks Zapp Brannigan is a military genius. Later, "Hmmm, odd that he would fall for an enemy trick like that." (Note in this case, because the character did great on almost every other lore roll, the other NPCs assumed he was being sarcastic when he treated the bad military leader as a good one with unfortunate luck). We milk the failure for all it's worth because it makes the session more memorable and quoteworthy. I guess it's because we quickly got over the idea that the DM and PCs are adversaries, cause they are not.