It seems to me that even when a thread is grave bumped...it could be relevant to someone somewhere.
A "thread age" warning would be cool if it were easy to implement. Most of the people I see gravebumping are new members that don't notice the date and probably just did a search for a topic.
Warning: This thread is 10 years old, are you sure you want to bump it? I react to old threads but I don't usually post in them.
Or dates bolded over 1 year with no new posts? Idk how customizable this site is, but I do let people know if they are new when I see it.