The 1 September after a qualifying young person's 19th birthday: false by default for Universal Credit, absent for Pension Credit #2291

What is wrong

A young person in non-advanced education or approved training is a qualifying young person "up to, but not including, the 1st September following their 19th birthday": UC Regs 2013 reg. 5(1)(b) and SPC Regs 2002 reg. 4A(1)(b), in the same words. The model treats a 19-year-old three ways:

So the same family gets a different answer from the calculator than from the microdata, and Pension Credit does not encode the date its regulation sets.

Fix

Since #1899 and #1904 the model places a date of birth (date_of_birth, or age and months_since_last_birthday). #2279 uses it for the 1 September after the 16th birthday. Do the same at 19:

• add is_before_first_september_following_19th_birthday, true when the fiscal year starts before that 1 September (a year counts if any of it falls in the period, as Count 16-year-olds outside education as UC and Pension Credit qualifying young persons until the 1 September after their 16th birthday #2279 counts the 16th-birthday period);
• make is_before_universal_credit_qualifying_young_person_terminal_date follow it unless set;
• add the terminal-date condition to Pension Credit, reading the same fact.

Every 19-year-old (age on 6 October) is before that date at the start of the year, so the default becomes "counts", which is what the microdata and Pension Credit already do. A dataset or user can still set either variable to false.

policyengine-uk-data need not change: its derivation gives the same value the formula does for the records it sets true. It becomes redundant.

Needs #2279 (it edits the same Pension Credit variable).