Seamless age (xid) replacement

Hello!

I need to use the 'age (xid)' function, but I have noticed that it is
deprecated without a clear alternative. I know that xid is also kinda
deprecated, so it makes sense not to use it. I can get xid8 from
'pg_current_xact_id()', which replaced 'txid_current()', but cannot use it
right away with 'age'.

I can cast xid8 that I've got to xid and pass to 'age', but 1) I have no
idea if it's the right way, i.e. it's promised to work or will work anyway
by accident, 2) 'age' is anyway deprecated.

I can re-implement 'age' by myself. It's (mostly) a subtraction after all.
But it would mean that I inline implementation in place of "api" function
call which is not always a great idea.

Could anyone advise, please?

Kind regards,
Ivan