How to define a custom type for two dates and extract years from it in PostgreSQL?

I want to create a custom type in PostgreSQL that combines two DATE fields (e.g., start_date and end_date).

And I want a SELECT query to extract just the year parts from these fields.

Given the following data:

The desired query result should be:

Update (after almost 8 years)

I don’t see a practical use case for creating a custom type to combine two dates.
The original problem could likely have been resolved using the DATERANGE type.

Here’s how it could be implemented using DATERANGE:

CREATE TABLE date_ranges(range DATERANGE NOT NULL);

INSERT INTO date_ranges VALUES ('[2010-01-01, 2020-01-01]');

SELECT EXTRACT(YEAR FROM LOWER(range)) AS start_year,
       EXTRACT(YEAR FROM UPPER(range)) AS end_year
FROM date_ranges;

SQL DEMO

CREATE TYPE twoYears AS
   (year1 date,
    year2 date);

DROP TABLE IF EXISTS myTable;  

CREATE TABLE myTable (
   ty twoYears
);    

INSERT INTO myTable VALUES (ROW('2010-01-01', '2020-01-01'));

SELECT (ty).year1,  (ty).year2
FROM myTable;

SELECT EXTRACT(YEAR FROM (ty).year1),
       EXTRACT(YEAR FROM (ty).year2)
FROM myTable;