In DOPs and solver SOPs (which are DOPs, hehe) I usually just create some random attribute and add to it, sometimes as simple as...
if(something something) i@myage += 1;
...or alike. I think mane people get stuck trying to use stuff that's there - and if it is and you know about it, cool, but it really is as simple as setting this up purely arbitrary - though kinda depending on what you do, you might want to not stack up and pass on too much data with your geomery. Usually this isn't an issue, but if you're doing huge particle setups or FLIP fluids or something, and you have 10 random vector attributes piped into the sim, that'll quickly start eating memory if you have high point numbers - but in regard to how to control stuff, you can just make s**t up as you go along, hehe...