On ageism- it exists, but there are also other explanations on why we see relatively few older people in IT. One is just the rapid expansion of tech in general. In 1997 the number of people working in "Computer, Mathematical, Operations Research, and Related Occupations" was 1,832,390. In 2019 it was 4,552,880. Most people entering any given profession are young, so you'd just expect to see roughly 2.5x then number of young people to old people (yes, I'm abusing statistics, but I think it is roughly right). What's more, it is absolutely true that older workers are more likely to exit to other categories like management or sales than they are to reenter the straight up IT workforce. You can explain quite a lot of the "youngness" of the workforce by non-malicious means.

Ok, that out of the way- I do believe there is an expectation that you are able to do different things as you age in IT. When you are early in career, the expectation is that you do your job well. Later in your career, the expectation is that your job very well AND you help other people do their jobs, too.

I think you are right- learning another SIEM tool isn't going to be fun, and isn't even what others will expect of you. But being able to evaluate that SIEM tool, understand where it fails against older/other tools, and helping close the gaps- that's probably more interesting and rewarding. Helping that fresh college hire close the gap between what they learned in school and all the extra stuff you have to do in the real world. Helping to org navigate the regulatory requirements of a specific industry. These are all things that really only come with experience.