I have two cats, both 12ish years old. One is long-haired and quite sensitive; if you change her litter brand or her food and/or don't clean the litter often enough, she's likely to vomit. Now that I'm better at keeping things the same/way she likes it, she doesn't vomit as often anymore.

However, my male cat is a pig and sometimes will eat too fast or too much and vomit almost instantly. I think of it as his swallowing air or something so his eating mechanisms go, "TILT!" and he throws up. But he doesn't do that too often either. I think sometimes they just have a "thing" going, something doesn't sit with them right, who knows? Cats don't have much to "do", I know my male cat eats out of boredom often.