Hello, Can someone recommend the best way of calculating age in years, mont

You're going to use the year(), month(), and day() functions to get the differences between the 2 dates. So you'll get this:
local!yearDiff: 1,
local!monthDiff: -6,
local!dayDiff: 1

Now, you'll check local!monthDiff. If it is negative, you subtract 1 from local!yearDiff, then add it to 12 (e.g. 12 + (-6)), and set that as the new month value. Then check local!dayDiff. If that is negative, you'll subtract 1 from local!monthDiff. Here's the tricky part, you need to figure out the number of days in the month immediately preceding the end date.

To do this, use day(eomonth(ri!endingDate),-1). This will get the last day of the previous month. Add this to local!dayDiff (in your example you can skip all of the day-related calculation because local!dayDiff is positive.

Now you have the 3 numbers, and all that's remaining is to concatenate them into a string:

local!yearDiffFinal & " years " & local!monthDiffFInal & " months " & local!dayDiffFinal & " days"

You're going to use the year(), month(), and day() functions to get the differences between the 2 dates. So you'll get this:
local!yearDiff: 1,
local!monthDiff: -6,
local!dayDiff: 1

Now, you'll check local!monthDiff. If it is negative, you subtract 1 from local!yearDiff, then add it to 12 (e.g. 12 + (-6)), and set that as the new month value. Then check local!dayDiff. If that is negative, you'll subtract 1 from local!monthDiff. Here's the tricky part, you need to figure out the number of days in the month immediately preceding the end date.

To do this, use day(eomonth(ri!endingDate),-1). This will get the last day of the previous month. Add this to local!dayDiff (in your example you can skip all of the day-related calculation because local!dayDiff is positive.

Now you have the 3 numbers, and all that's remaining is to concatenate them into a string:

local!yearDiffFinal & " years " & local!monthDiffFInal & " months " & local!dayDiffFinal & " days"