Every now and then this happens in the forum, the information in the older post are often obsolete or irrelevant.
Mechanism of 3 obsolete flags voted, and its gone
Who is going to maintain that obsolete flag? Although 1 year is arbitrary, it is better than the current situation.
Marnix suggestion to be able to mark something as obsolete would be safer implementation, as there is really no saying after which amount of time information would become obselete. Especially if other users can mark someone else's post as obselete so that inactive user's post can also be marked.
"Often" but not always, a year isn't really a benchmark for what people are searching for when it comes to information.
An option to mark posts as obsolete would be helpful. With the possibility to assign a modeler version which makes it obsolete.