How to map functions across objects/arrays in SQL?

Question

Say I have some data in table, which has the names and ages of customers who came into a store each day (the id functions as a unique day identifier).

id, obj
-----------------------------------------------------------------
1,  [{'name': 'jenny', 'age':22}, {'name': 'adam', 'age':32},...]
2,  [{'name': 'adam',  'age':32}, {'name': 'beth', 'age':27},...] 

What I'd like to do is find the average age per day

SELECT id, AVG([o['age'] for o in obj]) AS avg_age
FROM t

And the desired output

id, avg_age
--, -------
1,  27
2,  29.2 

This obviously doesn't work because the python-like list comprehension doesn't work in SQL. What is the proper way to do this in SQL?