As a midwestern American (Iowa), I want to understand the history, reason, and mechanics of why southern Americans say "whenever" when the word "when" would suffice.
An Iowan (and the rest of the West and Midwest, probably) would say:
"When I was a child I loved candy."
But, someone from Alabama, Georgia, and North Carolina are more likely to say:
"Whenever I was a child I loved candy."
Where I grew up we were taught that "whenever" is used to describe an unknown when, either in the present or past. The other situation where whenever was appropriate is when discussing a "when" that occurred multiple times.
Ex 1: (past repeated)
"Whenever he decided he wanted to dress like a girl, he would put on his pink tutu and just dance the day away."
In this tense, whenever indicates that something was repeatedly done but specific dates and times aren't being offered. This is a generic, summary "when".
Ex 2: (future unknown non-repeat)
Jim: Hey, what time are you leaving today?
Bill: It depends.
Jim: Well, whenever you decide to go, can you pick us up some milk up from the store before you come back?
In my understanding, both of these two examples would be considered correct usage of "whenever".