I've had this platy since about this time last year. I got it fairly young too, so it isn't like its lifespan is over.
Over the last few days his fins have been clamped up and he has been hiding a lot and gasping at the bottom of the tank. I found another BIG male platy nipping at it. I thought this may be the cause, so I got rid of the male by putting it in with the danios. A day has passed and it seems worse.
I hope this platy doesn't die yet, it's one of the first fish I had and it has fathered.. too many platies lol.
All other fish are fine. There hasn't been ich in the tank for months now. Aside from his clamped fins and gasping, he looks fine and is eating still. He wobbles while he swims, though.
I'm hoping it might just be an unseen injury he got from the male platy.
Edit: I have been dosing the tank with aquarium salt over the last few water changes, and it seems to have made the tank more active.