Why doesn't 'clear' fit here?

[Watie]

English Language Tests, Intermediate level

ESL/EFL Test #69 "How to compliment", question 6

I honestly can't believe that you are ......... enough to have such grown up children.

(a) wise
(b) old
(c) grown
(d) clear

English Language Tests, Intermediate level

ESL/EFL Test #69 "How to compliment", answer 6

I honestly can't believe that you are old enough to have such grown up children.

Correct answer: (b) old

Your answer was: incorrect
I honestly can't believe that you are clear enough to have such grown up children.
_________________________

Hi Teachers,

Why doesn't 'clear' fit here?

Thank you.

[Mister Micawber]

It just makes no sense to me, Watie. What do you think 'clear enough to have grown children' could mean?
_________________
Native English teacher at Mister Micawber's

[Watie]

Please, my apologize to you..
Sorry, I had read in different meaning and I knew I was wrong. I read 'have such grown' as present perfect (It is clear that she has grown up from children to become a man.) and 'to have grown children' means possessive (having a children) instead. ;)

[Mister Micawber]

That's right.
_________________
Native English teacher at Mister Micawber's