"What do you want to be when you grow up?"

The usual question and answer seem to be of the form

What do you want to be when you grow up?

I want to be a singer when I grow up.

Should it not be

What do you want to be when you have grown up?

I want to be a singer when I have grown up.

Here we have interpreted grow up as the process at whose end one becomes a singer. Should the first pair be considered correct simply because of its accepted usage, or is there an alternative explanation for this?

Solution 1:

No, because a present tense is normal for an achievement in the future:

When I am ready

When I get tired

When I reach London

In all of these a perfect is possible ("When I have reached London" etc), but not required.

"Grow up" can be a process, but in "When you grow up" it is, at least notionally, an achievement (i.e. end of a process).