Alexrey - whether or not you are a British citizen still doesn't change the fact that right now we have pilots on 2 year holds waiting in the training system. To give you an idea of how few spaces there are in the training system and how many pilots they are trying to get through, we have just had a holding officer posted in to us for a full tour between his basic and advanced course. Not a normal hold, a full 2 year tour as a baby staff officer.
I wouldn't make all your plans around becoming an RAF pilot, especially if you are already 23/24. Unless you are already in the system, you would probably need to be closer to 20/21 to have a fighting chance of making the age brackets for starting pilot training given how little requirement there is for new pilots at the moment By all means, ask the question, but be prepared for an answer you don't want to hear.