David didn't use to eat vegetables when he was a little boy.
On the condition that this sentence intends a past time meaning, which means that we finished to do something, then we can't use present perfect as seen.
David didn't use to eat vegetables since he was a little boy.
Now it intends the meaning that is still in progress, David still doesn't like eating vegetables. Can you point out what I'm actually missing?
If he still does not like eating vegetables, you have to use "since",so the first sentence is correct
If you use "when", it shows that he hadn't like to eat before, but now he likes
and you must say "didn't use to" not didn't used to
If you want to say something about the past you can use the simpler sentence
David didn't eat vegetables when he was a little boy.
That has no connection with the present, but you can make it so with
. . . and he still doesn't like them.
or
. . . but he likes them now.
