One father wants to say to his little baby something like:
If you work very hard when you grow up then you will achieve success.
If you work very hard when you have grown up then you will achieve success.
Is the difference between the meanings of the sentences?
Idiomatically both mean the same, the first sounds how I would express it. The second could be used to mean "the process of becoming a success will only start after you finish the process of growing up". I probably wouldn't use the second one in the context.
This is somewhat idiomatic. "When you've eaten your dinner you can have your pudding" is correct and the present perfect serves mean "when you finish eating..."
As I noted in a comment, you should but a comma before "when". It helps avoid the reading of "When you work very hard at growing up". Ambiguity is sometimes good, but here you can avoid it with a simple comma.
