I can confirm that these statements just don't ring very true at most major technology companies; it may be a thing specifically for startups which I have little recent experience with. I know plenty of people in FAANG, Microsoft, Salesforce, etc. that are still ICs that are well over the age of 35.

Ageism may be alive in startups, but in technology as a whole, it doesn't really seem to be a big deal if you are up to date on your skills.