I think the record is something like 7 or 8 minutes? I've seen someone who can stay down for a couple of minutes. Sitting calmly in a chair I can hold my breath for a minute and a half after hyperventilating, but if you do it wrong you can pass out and drown. Swimming, I think I can hold my breath for half a minute or so. My point is not to boast of my "prowess" (half a minute: wow) but that you can have loads of fun free diving short dives.
Before scuba diving I used to be able to free dive no deeper than 15 feet before my ears hurt. I could equalize, but not beyond that point. After scuba diving, maybe my technique improved, but I got down to the bottom where it was 40 or 45 feet.
Maybe the trick for me was to equalize constantly on the way down, rather than in spurts.
As with anything, the trick is to practice. But please remember to take it little by little and don't exceed your ability. If you drown because you tried to go too far too fast you'll have lost a whole lifetime.
And again, I had loads of fun free diving to 12 or 15 feet.
As for fins: Your fin size and style should match your leg strength. Bigger fins are more work to kick. If your fins are too big you'll just waste your air. Don't be fooled by looks into getting the wrong fins for you.
