postgresql – how to recover late claims using join two tables

First table

Complaint_id Completetion_date Templateid
53035 2018-11-16 00:00:00 5
47956 2018-11-03 00:00:00 13
3953 2017-11-27 00:00:00 17

Second table

Template_month id
8 5
6 13
4 15
2 17

In the first table, the date of completion is November 16, 2018 and tempalteid, the 5, and in the second table, id. 5: 8 months means that you have to calculate 8 months from November 16th and that the complaint is not late. In the second line of the first date of completion of the table: 2018-11-03 00:00:00 with the model identifier 13 and in the second table, 6 months ago; the periods are late, then in the result, 3953 is late