My main priority is to try to keep up with my current photos, partly for me, but mostly for the demanding grandparents who live halfway across the country.

I put the pics up on a website for them to see. It is also easier to journal (something I really need to work on) if the events in the pictures are fresh in my mind, so that's another incentive for me to try to keep up. If you were good about keeping a diary or something like that (which I'm not), you could just refer back to that later though.
As time allows, I'm going back and picking some of my favorite older photos to work on. I think I would be totally overwhelmed if I tried to scrap everything, so I consider the older pics to be just sort of a fun change of pace from my current ones. I doubt I will ever get through everything. I've even got a huge stack of slide reels from my childhood that I borrowed from my folks. I plan to start doing a few of those soon too.
I don't see a problem with jumping around though. Scrapping should be fun, so I think you should work on whatever inspires you at the moment. You can then organize the finished products as you go in a way that will make sense for later on. For the older photos I'm working on, I plan to post them as I do the pages, but also have them listed by date and by subject, sort of a cross-reference kind of system.