The woman seemed to imply I couldn't buy missing years for when I've been opted out...
This is correct. Opting out didn't mean you missed a years 'stamp' - You still paid NI and you still got the stamp. HMRC then paid some of that NI money into your 'contracted out' scheme in exchange for not adding to the SERPS part of your SP. You can only buy back years for which you are completely missing the stamp - for instance if you were in full time further education (university), or living abroad, or not working and not claiming benefits. There is also a time limit - I think you can only go back something like 7 years. So if you haven't missed an NI stamp in the past 7 years there is nothing you can buy.
Your state pension age is at least 67. It is supposed to be going up to 68, but the legislation for that hasn't reached parliament yet. There is (another!) pension review going on at the moment due to publish in 2017-2018, and it's likely the results of that will be what is enacted. The govt have said that future changes won't affect anyone within 10 years of their current pension age, so if it goes up it's likely to come in in 2028 or thereabouts.