Your post makes sense: After all, sites like cwjobs delete your job advert after 28 days (and you could be paying anything upto £250 to post it), and other sites such as Monster typically do 30 days. Hard to fill jobs can be left open for 60 days but are not typically viewable due to the large amount of new postings.

Since Qt Centre doesn't get as many posting as either of the sites above, 30 days seems a little short, but I agree that 6 months seems too long. Possibly 60 - 90 days? and yes, close the topic instead of deleting it. If someone is determined, they can still PM the thread poster. Its better than having all the job posting for the past 10 years float to the top of the "New posts" window.