Meauring time and months AND if statements.

Hello :)

This measure I wrote helps work out the data’s age in months

_Months_of_age = DATEDIFF(MAX(SIR_XLS[Rev_Date]),TODAY(),MONTH)

What I would like is something that, where there IS a date, returns the age in months, and if there is NO DATE, to say,

“No date supplied”

Any ideas how would I write this? Is this an IF statement sort of thing?

Thanks in advance for any help or pointers you can give.