Welcome to HCM,
At the age of 81 years swimming for one hour is not advisable.
Again you get breathing problem while doing some strenuous work indicates that you might have some coronary insufficiency.
Getting problem of having difficulty in walking might be due to some cerebral insufficiency, might be due to high blood pressure
Go for ECG and blood pressure checking.
Afterwards go for swimming 25-30 minutes only and with light swimming.
Ok and bye.