Junior dev:

Straight out of uni, know the latest developments while having also studied long established standards and specifications (like POSIX, LSB, SQL, etc), full of energy, and ready to speedrun burning out any %

Senior dev:

Hasn't learned anything substantial in decades, uses outdated specs because "who got the time for that, and legacy stuff works just as well anyway", copy pastes most of their work from stack overflow, is only still employed because of their inside information knowledge and the utter absence of documentation leading to a bus factor of one, and has perfected the art of gaming the system to the point of photoshopping a sloppy IDE screen over their WoW game whenever a picture of them "working" gets taken.

Yeah, checks out.