Hi there. I run a social/casual raiding guild on the joint realms of Lightbringer/Mazrigos. We’re an 18+ horde guild and the average is * cough * a tad older than 18 
We raid twice a week, generally (occasionally someone will organise an additional one for transmogs, achievements, alts, etc).
Our standard raids are on Wednesday and Friday evenings, 9.30pm to midnight server time.
We have no requirements for people to raid … ie, yes, we have a minimum gear level and expect people to gem, enchant, be prepared, etc; we don’t, however, expect people to attend a specific number of raids.
We put raids up on the calendar in-game, people sign if they want to go, and we accept them on a first come, first served basis. If there’s space, and you want to go, and you can fulfil the raid requirements … you can go.
Most (if not all) guild members have complicated lives, with jobs, dependants, chores, etc … we understand that stuff happens so we’re pretty flexible and relaxed. Many members have multiple characters/roles so we can usually accommodate changes fairly easily.
Of course, we’re not just a raiding guild … we spend more time not raiding than raiding, and not everyone raids, or raids regularly … we have people who run mythic dungeons, mythic plus, transmog runs, island expeditions, invasions … there’s usually something going on … even if it’s just a chat in guild whilst we’re all doing fishing, pet battling or quests
If this sounds of interest, check out our website at www.darkwolves.eu
you can read more on our realm forum post too (although when I say “more” … I do tend to waffle on a bit, so actually I’ve probably already covered most of it here!):