Others have covered the main bits. But as someone else who has often been treated as young… it’s also possible to roll with it. Talk less and when you do talk, make it more about reflecting what someone says back to them. Then you’ll be perceived as young and smart instead of young and naive.

But I personally enjoy the fact that at over half a century, I can still hang out with people of any age and they feel like they can be themselves with me. Even if people in their 70s still treat me like a child.