I have only had to worry about simple ER and hence this limits the choices for A14 that I have had to consider in the past.
HOWEVER I have just ditched A14 rather than trying to convert it and just tried to populate A71 as a fresh field:
If the learner is 16-18 use 01 in A71
If the learner is 19 or more and A69 is not set (ie is 99) then use 02 in A71
If the aim is not funded (can't think why) use 99 in A71
I use A27 and L11 to calculate the age, with A27 against the Program Aim being the earliest Start Date (and a fun algorithm to get the age right and allow for leap years).
Now I do have some information on the relationship with A69 (having corresponded with the Data Service on this):
If A69 is 01 then student must be 19-24 and then A71 is 01
If A69 is 02 then student must be 19-24 and then A71 is 01
If A69 is 03 then student must be 25+ and then A71 is 02
A69 cannot be set to any of the above values if the age does not correspond correctly
If A69 is 99 then use the rules for A71 that I stated at the start
Hope this helps some.
I note that there have been requests from Providers to retain A14 but that the Data Service et al do not require it and so have declined to retain it (helpful!). It could be stored in one of the Provider Specified Learning Data fields (A48 or A72) and then at least you can report on it and check it and also see it on the PFR.
Thanks,
Caspar