Functions in macros - syntax

Hi! I have posted this in slack support channel but I am not sure if that’s the correct place. Apologies if I am mistaken.
Can anyone point to the right direction with jinja? I am very lost with it. I want to do a simple function where a number is calculated using dates. This is an sketch about how I would do it in SQL, any links/tutorials welcome. I have not been able to find something related, not even in dbt documentation or through this discourse. Thank you!!

CREATE FUNCTION test.get_account_age (
							trade_type VARCHAR(20),
							account_number INT

    DECLARE account_age INT;
    DECLARE date_diff INT;
    DECLARE datetime_check1 DATETIME;
    DECLARE datetime_check2 DATETIME;

    #get date to use based on trade type
    IF trade_type = 'type1' THEN
		SELECT datetime_check1 =  orderdatekey FROM ordertable;
   # if trade type, etc...
   	END IF;

    #get global date 
    SELECT datetime_check2 = first_date FROM accounttable

    # get difference between dates
    SET date_diff = DATEDIFF(month, datetime_check1, datetime_check2);

    # calculate account age
    IF date_diff < 12 THEN
		SET account_age = 1;
	#ELSE IF date_diff >= 12 AND date_diff < 24 THEN
	#	SET account_age = 2;
		SET account_age = 0;

    RETURN (account_age);