Would it be stupid for 2 people that are inexperienced in speedrunning (me and a friend) to attempt an all advancement speedrun?
As a casual / for fun run? sure why not.
As a speedrun? just a bad idea. you're not gonna finish it because some advancemants are very hard to do without knowledge of a setup and could take tens of hours in of themselves - nevermind keeping track of stuff like all biomes, eating all foods and breeding all animals along with getting a conduit, god apple
I'd highly recommend starting with random seed glitchless (RSG) 1.16.1 to start building up the game knowledge to do some of the slightly longer categories
I wouldn’t call it a speedrun.
Speedrunning AA requires intense multitasking (all foods, nautilus shells, biomes, etc.) and I doubt you would do that all at once, rather doing them one at a time.
Additionally, a speedrun requires you to do it in one sitting… Probably the hardest advancement, HDWGH, requires a specific setup to be able to do, and being “inexperienced,” I assume it’s not something you know.
If you’re doing this as a challenge on a server, you could always look up the setup; however, in speedruns, this is something you can’t do.
TLDR: AA is HARD. This is something you and your friend can try to complete together on a server or LAN world together as a challenge, but speedrunning it is very difficult.
All Advancements is officially segmentable (even for co-op), so you'd be allowed to do it in multiple sittings. There's no reason why it would be impossible for two inexperienced players to do it as with multiple sittings there is theoretically infinite time, but it would be insanely difficult and probably take ages to do.
There's plenty of things you can practice for AA, and each of them would save you so much time in the real thing, as well as a guide here https://docs.google.com/document/d/18Iurqcqi3L6LujgMxjO15w66oM_8r5HnFwPNVGR9yk4/edit. I'd recommend doing this and watching several AA runners streams first, and definitely try to complete an any% run before attempting AA.
all the answers here are very enlightening... also it taught me something too.
don't try "casual" AA speedrun with a friend if you're both noobs. Unless it's just to challenge yourselves 😉