This may be a stupid question, but I really don't think it is. I really think some people do care about age and/or gender (for both Extinction and MP). I can totally understand people not wanting to play with little kids, or little kids playing with older people - I can see how that is weird and strange.
For me, so long as you're not singing or shouting, and you can listen to advice from people (or give it well, and not in a bossy manner), then I do not care of your age or gender. I never ask people if they are male or female, or how old they are. If someone was acting too immature, to the point of I didn't want to play with them cos the game was not fun etc. I wouldn't ask how old they were, I'd simply assume and just back out.
So, do you have any age or gender (or other similar) requirements for people that you play with?
Gender: Absolutely not. Anyone is welcome.
Age: It's not so much the age as the maturity level. I've met many players who are self-proclaimed U18 players who have been fantastic people to play and chat with. I've also met my fair share of +18 players who have had a level of maturity comparable to that of a young child. The other day, I got into a lobby with a gut claiming to be +18, but he said my name literally 5 times in 2 sentences. Not Mature...
I don't care as long as they can kill aliens/people as the case may be.
That being said, I haven't played extinction with a female that has done very well (as far as I know). I know they exist, but I haven't met them.
Age-wise, I feel a lot like Gram. Maturity isn't completely parallel to age. I was very mature for my age due to a lot of shit that happened in my childhood that forced me to grow up. But in some areas I haven't grown in maturity since then
I've played with some younger folks that are pretty good, I've played with some that aren't. As long as they don't talk the entire time/want to share their life story with me upon first meeting me, we'll generally play alright together.
TBH, I don't give a damn about who I play with, as long as they play the game properly. The majority of people on my friends list are younger than me and have shown me a trick or two when playing, I enjoy messing about and having fun, but I do like to complete the task in hand and as long as they're doing that, then I'm okay with it.
Even people who i thought must be atleast 18 when i asked them they say like 14,15,16 or so.Even little kids can sound older than they are but i don't mind playing with women most of the time they don't use mics anyway so you wouldn't know if it was one, i don't really like playing with little sqeeky kids as they do me head in,some are not that bad mind they actually listen unlike some adults do!!
Gender: Makes no difference, as long as each is able to talk co-operatively with each other (there are quite a few shy people out there), then it's all good.
Age: As others have said, I would class it more as their 'maturity' and ability to co-operate and, most of all, BE NICE. I have 18+ and 18- people in my FL. Some are even only 12 years old and such, but they are mature, good players, and enjoy themselves when they play. They don't make it feel awkward, they just want to play the game as it was designed, to BE played.
Everyone on my FL I have huge respect for as gamers, whether they are male, female, voice hasn't cracked, or voice sounds like a trombone.
Gender, not at all. But I have yet to meet a female extinction player.
Age though, it's different. If they have a mic, and they're communicating, it's usually alright if I have three experienced friends with me. I actually like it, it brings a refreshing, often humorous mood to the game when usually it's pretty silent.
But yeah, I agree playing with split screener 8 year olds who sound like they're just hogging older brother's PS4, I usually back out. Or I will back out on a kid when I'm not in the mood to corral and teach someone.