Speaking as someone who is a 40+ IC Eng at one of the FAANG companies (and previously worked for another) let me give you some advice:
- First, at the risk of being blunt, you come across as someone who needs to get off their high horse with your list of "demands".
Take the open office. This is the norm. IME this has always been manageable with headphones. YMMV.
- The biggest issue is not wanting to exhaust yourself helping others. Helping others is about your best value add. What's more, helping people is a pretty good way of earning the gratitude of your colleagues.
Some general thoughts on working as a 40+ IC in these companies. Again YMMV:
- I don't tell people my age. Nor do I allow people to infer it by, say, mentioning when I graduated college or make references that would otherwise indicate my age. Now I don't look 25 but do people assume I'm old looking in my 30s or in my 40s? I have no idea. I think it's in my best interest not to find out.
- Ageism is very real and it's subtle. I've had directors tell me "I like new grads so I can mold them" without realizing that's brazen ageism.
- Culture fit is another common proxy for ageism. You can say that millennials will naturally gravitate to those of similar age or background. Grads from one college will tend to prefer grads from the same college. Common experience is one reason for this but another is people can overvalue the social proof of, say, being an MIT or Stanford alum as that by extension increases their own value.
Culture fit is problematic on many fronts and tends to exclude those of nonstandard backgrounds for which age is but one factor.
- With or without justification you will have to alleviate the concern that you aren't an old dog who can't learn new tricks. Some older workers will expect deference based on age (as a proxy for seniority/experience) but it's the nature of the beast that in FAANG companies you may end up reporting to some wunderkind who is 2-3 years out of college and may be 20+ years younger than you. If you get hung up on that you're going to have a bad time.
- Likewise older workers will have to fight the stereotype that you'll be less committed because of other responsibilities (typically meaning family). The way you're wording things here does you no favors because it can come across as entitled and inflexible.