I'm also 74, and I too have always been physically active (e.g. bicycling, skiing, hiking, swimming). I was told I had a heart murmur when I was in my 20s, and I was diagnosed with HCM based on echocardiograms and MRIs when I was about age 66, but I never felt any symptoms until age 72, when bouts of SOB (shortness of breath) suddenly seemed to come from nowhere.

Good luck remaining asymptomatic, but if that changes, then you, like me, are fortunate that you already have the diagnosis, so you will be able to consider appropriate treatment options right away.

(Ultimately I opted for a septal myectomy in July 2025, and within a few months I was back being active.)