My son, 2 and a half, clearly does not grok the concept of waiting for something.
If he asks for something, and I say "okay, I'll give you x right after we finish doing y", he'll say okay, and then continue to ask for x throughout activity y (even if it is something incredibly short, such as "I'll hand you your toy as soon as I'm done buckling you in to your car seat", which will still prompt 2-3 polite additional requests for me to hand him the toy while I'm buckling the seat belt).
Similarly, the concept that we're going on vacation "next week" seems to be one that he doesn't understand.
I get that there are cognitive milestones involved here that he simply may not be old enough to have reached, and I'm not complaining or worried. However, I am curious as to when he'll be able to understand waiting, and what, if anything, I can do to help teach him the concept of patience.