Sort Order Doesnt Work on Custom Field (numeric value)

I am trying to sort AE post blocks using a custom field which has numeric values. However it doesnt seem to do it correctly . Looks like it is considering the numeric value as text. To explain it more clearly, i am trying to list doctors with varying years of experience and sorted in descending order by number of years of experience . This is how it is ordering it

DR C – years of experience – 9
Dr E – years of experience – 7
Dr F – years of experience – 4
DR A – years of experience – 31
DR D – years of experience – 18
DR b – years of experience – 12

Which should be ideally

DR A – years of experience – 31
DR D – years of experience – 18
DR b – years of experience – 12
DR C – years of experience – 9
Dr E – years of experience – 7
Dr F – years of experience – 4

I am assuming it is considering these numeric values as text. I am using ACF . Please suggest