Possibly A. Or B. Or neither. I don't know... what IS a domainer? Am I one?
I'm a domain owner, yes. From the beginning all domains I bought were intended for own development - business ideas I had, and in some cases realized. Others ended up dormant, if I never found time for that specific project, or didn't find it worthwhile. Sometimes I dropped those domains, not even thinking about that there was an aftermarket for domains. I didn't realize that until a few years ago... even though I sold my first domain, (which even WAS my first domain), already 1999.
Thinking back, I'm rather sorry I dropped some of them. Or didn't register others that I thought about at that time. But it's STILL so that I hardly ever sell a domain... I develop them, or sit on them until an end user with big pockets shows up. Flipping domains for peanuts isn't for me, and generally ignore any offers from resellers to buy domains I own.
I really think that I'm more of an end user myself than a domainer, even though I've bought quite a few domains for speculation, not really having an end user idea for them, but that tends to change from time to time, when I come up with ideas for domains that I had no inkling about when I first bought the domain.
Counting one way, I've been domaining for 14 years. That's when I started registering domains. But I didn't realize the value of domains as an asset in themselves until perhaps 5 years ago... but still, I see domains more as a mid-term investment, not as a day-to-day living.
So to count an average on how long people stick with domaining, one first have to define clearly what domaining and a domainer really is.