Most people have most of their children bewteen the ages of 20 and 40, but there are lots of exceptions.
If 1) Your parents dropped out of high school to have you when they were 16, in 1966, and you continued the family tradition by having a child, Matilda, when you were 16, in 1982
2) Your parents had another daughter, Esmarelda, when they were 42, in 1992
Now Matilda has an aunt who is 10 years younger than she is.
It is even easier with half-aunts and uncles; a man has a family when he is 18 - 36, they grow up, get married and have kids, the man divorces or his wife dies, he marries a 20-something and has a second family. The sons and daughters in the second family will be half-brothers and half-sisters to his first family, and half-uncles and half-aunts to the children of the first family. They could very well be 0 - 10 years yoinger than their half-nephews and half-nieces.
Step-aunts and step-uncles are even easier, since all the man in question has to do is marry someone WAY younger than himself who has brothers and sisters; no having to walk a crying baby to sleep in your 50's.
The wife of your father's brother is your aunt by marriage. You may have several, courtesy of the same brother, if he marries and divorces as often as a Hollywood movie star.
Your step-mom's sister is your step-aunt. Her husband is your step-uncle, if he is a decent guy, or "some creep in the family of my evil step-mother" if you don't get along with them.
The wife of your step-mom's sister would be her "lesbian partner" or just "partner". In 5 states she'd be her "wife".