Is ageism real in IT?

Sort of. But it works both ways. If you're 40+ you're expected to be able to lead or at least train. Which isn't all that far fetched an assumption. When you're 25, people will probably not want to see you leading but somewhere in the trenches, gaining real world experience.

If you market yourself correctly, age isn't a problem but an asset. That might entail getting a suit though. But you'll get a raise in paygrade to compensate for that.

I think it's more prevalent in IT. If you aren't a 25 something knowing the latest front-end framework, you're are considered old already. I don't know any 40 year front-end developer.