I often free dive alone - not because I can't find anybody to go with me, but because I want to. I know it's potentially risky, but experiencing the ocean without the distraction of others is something I love too much to give up. Is this stupid? That depends on your point of view - personally I'd rather live life to its fullest and accept the risks that come with it.
It's worth noting that I don't have a wife or kids. My perspective might be different if I did.
As for "limits"? When it comes to free diving, it's a bit of an abstract term. No free diver knows his/her limits. Until, of course, they break them, which often involves drowning (especially if you're by yourself). As such, claiming to not push your limits is inherently foolish, but we try.
While diving, my goal is to enjoy myself (and maybe catch dinner), not to "train" or set records. Training for any sport implicitly involves pushing yourself, which can have very bad consequences for divers, as too many people have found out. This isn't anything I have a desire to do.
As for me? I never stay down longer than I am comfortable - if I feel out of breath once I reach the surface, then it's been too long. This doesn't translate well into depth/time parameters, since there's a lot more that goes into a dive than just that. And no hyperventilating - tricking your body into ignoring its own oxygen levels IS dumb. Personally, the deepest I've gone while alone is around 75'-ish, and usually it's 50-60 max. The real reason for this is that there aren't many accessible spots on the island that are deeper than this and worth the effort.