To be fair, with no data to back it up, this is just an anecdote. So saying it’s stereotyping ageist bullshit is a perfectly valid response to it. I just felt it fit the question quite well so I went and dug it up and shared it. If you feel differently, no stress!
The reality is going to be different to everyone, and it’s as much a learned behaviour as anything else. It’s not like collectively an entire generation got together and decided “it’s ‘no problem’ now instead of ‘you’re welcome’, okay?” Language evolves over time after all, and knowing why that happens and the actual causes for it are something that will require a lot more analysis than a couple of anecdotes from the internet.