I'm not quite as bad as some others as I can swim and actually enjoy it but I will defend some that claim to "sink" when in water. I too sink.
Some are legitimately constructed physically in such a way that they in fact simply sink if they are not moving: most folks naturally float. Those who naturally float are far more likely to have an easy time at swimming or even learning to swim. Those who sink (like myself) have a far more difficult time at learning and even when you do, swimming is far more of a workout than a typical "floating" person. That, I can assure you. It's the only thing keeping me from triathlons. I've been harassed to no end to get into it (I do other types of racing) but know that I would exhaust myself in the swim so.....
I was forced to learn to swim as a kid because we had a pool, a boat and we live against one of the biggest fresh water lakes in the world. I continue to enjoy life in, on and around water (kayaking, fly fishing etc. etc.) but I NEVER go out in the Kayak without my PFD. If I'm in heavy current and there is any chance of falling when I'm fishing, I have a tiny PFD that you can barely see as well that I wear under my vest. Pull the cord and it inflates.
Not being able to swim is something that I would personally try and correct at this age however ESPECIALLY if you work around water or your hobbies see you near or in the stuff. PFD's PFD's PFD's people!
Living where I do, I have MANY insane/scary/tragic stories involving water.
Some people sink. That's the truth.
When I first met my wife, she totally didn't believe me when I told her I sink. She was convinced she could teach me to float on my back and I told her it wasn't possible. I bet her 20 bucks I could take a huge breath of air and sit cross legged and arms crossed at the bottom of the deep end of the pool.....................nothing weighing me down. Just sit there. She took me up on it and I was 20 bucks richer. I took a breath, stopped moving and sunk right to the bottom. Once there, I sat down cross legged staring at her. She'd never seen it before. I'm relaxed as hell around water and still she could not get me to float. We tried MANY times. Not happening.
This came up in conversation once with some friends and low and behold, another buddy of mine is the exact same way. He thought he was the only one.
Sorry, that was way too long.
Back to the crazy stories............way more fun to read.