My 15 year old cat is doing the same. I read somewhere (might have been on here!) that as they age they get sort of tunnel vision and get easily confused when faced with lots of doors. Doesn't stop it being annoying!
My 18 yr old has started yowling. She is pretty deaf and I think that might be something to do with it. When she was younger, she would seek me out for company, now she prefers to summon me! (well, that's my theory).
Someone on another thread suggested yowling might be something to do with second kitten-hood, I do wonder if the miaow mine does is basically a kitten-call for mum, of course at her age that would sound like a full-on miaow.
I've been wondering about eyesight. I can imagine that failing sight might be a cause for confusion and anxiety in a older cat and unexplained vocalisation is one of the possible symptoms. Has he shown any others if you cast your mind back?
(I've noticed some possible behavioural changes in Seniorboy recently which might just be attributable to failing vision. (He hasnt got cataracts but who knows what else might be going wrong - at his age some macular degeneration at least would almost be inevitable.))