Now, before anyone says 'do a search' or 'read the stickys', I have done and also looked through the old seating queries et/domestic thread, but my question is probably so basic that everyone knows the answer.

But I don't often travel at the back in fact I think twice in the last 10 years plus, but we have to fly ET LHR BRU soon (no reward in CE open).

Why cant I select the exit seats ? I would have thought as a gold they would be open. The flight is over 6 weeks away and the plane looks empty at mo.