Knapp gave some really good advice. Only things I would add to his comments:
Check the audio recording laws for you state; if single-party consent is allowed, record your conversations with the landlard/manager(s). If you get to a point of having to communicate via written letters, the landlord/manager is usually going to take a harder stance.
I would contact your local Housing Authority and see what you can find out about your complex/landlord from them. Many times if there is 1 old person in a complex like this, it's a subsidized or low income unit situation. If that's the case, you will lose any complaints they make. You may offer to move units to avoid this person with highly sensitive hearing. Lastly, if you can record the noise from others, you can have some evidence of being singled out...