Being super lean and carrying mass in large muscles will ruin this, fwiw.

In my late 20s I was militantly fit and also very into rock climbing. I supplemented this with some lifting to balance things out; people who ONLY climb end up looking a little weird as the lats develop out of proportion with the rest of you.

Anyway, even with a lungful of air, my neutral buoyancy point was like 8-12" below the surface.

Alas, I am now 51.

Same here when I was younger (i.e., less fat). With a full breath of air in me, I'd float, but exhale a bit and I could sink to the bottom of a 12 ft pool without any effort on my part.

Only if they're not panicking and thrashing about.

true. it’s definitely easier said than done, but it’s a useful fact to have in your head