i think fixing them is best, it will take ages (while we are ) fixing them
It will take ages to fix them.
I put the verb some other way to find out the right answer but I am not sure I did it well.
It will take some time to fix them.
I know that a gerund form usually refers to the past.
e.g. It took me ages fixing them.
Is my answer correct?
Not a teacher.
We use these two structures to say how long to do sth:
-It + take + period of time + (for sb) + to do sth
-S + spend +period of time + doing sth
So I think 'to fix' is the best answer for the question. 'ages' here means great length of time (Ages Definition | Definition of Ages at Dictionary.com)
ages to ...