Being an aggressive driver isn't the same as having road rage. Road rage is "it's own thing" and involves rage. Aggressive drivers aren't always angry at all. A lot of them just think that driving in a non-aggressive (and more sensible) way is "driving like an old lady". A lot of others think (know) that a person can't always just politely sit and give everyone else the right of way, but they take it to an extreme in not knowing how to draw a line between assertive driving (or between temporarily and in isolated situations, being just a little more aggressive) and, instead, driving aggressively all the time and whether or not "just being a little more assertive/aggressive" when a traffic situation requires it.
Sometimes people who drive aggressively don't even realize that's what they're doing. They're happy enough and not angry at anyone. They're just sometimes people who don't have either the driving (and sometimes accident) experience, or else the spatial skills or awareness of how things can go wrong (and - yes - even to THEM, even though they operate under the "it won't happen to me" kind of thinking). I think aggressive drivers have one or more of the following things: 1) the ego to think they're smarter and better drivers than everyone else (so they don't have to worry about doing the most cautious things), 2) the ego to think they ought to always be first, and/or 3) an insecure enough ego that they won't do what's wise and instead do what won't get them thought of as "uncool" (as in "driving like an old lady").
Of course, some aggressive drivers are just hostile and angry people in general.