The three question marks are showing you that this array has three dimensions. If there was only one question mark, it would mean that the variable was declared as one dimensional. This is built in to VB and can't be change, as far as I know.
I think there's real value into making your code more readable and self-documenting. If I had a three dim array, I would probably create some custom class modules to model the objects that I was using.
If your first dimension is a SchoolID, your second dimension is a ClassID, and your third dimension is a StudentID, then code using custom class modules like this
Debug.Print Schools(10).Classes(3).Students(7).Name
is more readable than
Debug.Print arrLeeftijdenG5(10,3,7)
I don't know what you're storing, so it's just an example. Consider using custom class module to model the real-world objects your code is manipulating. There's a bit more set up involved, but it pays dividends down the road.
(24,5,8)to(0 To 25, 0 To 5, 0 To 8)in my dim in that case.