Replace volljährige_alle_rentenbezieher_hh with per-person Regelaltersgrenze check

[MImmesberger]

Problem

The variable volljährige_alle_rentenbezieher_hh is a household-level boolean that checks whether all adults are pensioners. It is used as a crude switch to separate Grundsicherung im Alter (SGB XII Kap. 4) from Bürgergeld (SGB II) and Wohngeld:

Transfer	Gate	File
Grundsicherung im Alter	only if true	grundsicherung/im_alter/im_alter.py
Bürgergeld	only if false	bürgergeld/bürgergeld.py
ALG 2	only if false	arbeitslosengeld_2/arbeitslosengeld_2.py
Wohngeld	only if false	wohngeld/wohngeld.py

This is wrong in two ways:

1. Wrong eligibility criterion. The law does not condition Grundsicherung im Alter on pension receipt. It requires reaching the Regelaltersgrenze (SGB XII §41 Abs. 1–2 referencing SGB VI §235). Early retirees who receive a pension before the Regelaltersgrenze are not eligible for Grundsicherung im Alter — they fall under Hilfe zum Lebensunterhalt (SGB XII Kap. 3, not implemented).

2. Wrong gating unit. Eligibility is per person, not per household. A person who has reached the Regelaltersgrenze is eligible for Grundsicherung im Alter regardless of the partner's age or employment status (SGB XII §41 Abs. 1). The current code incorrectly excludes couples where only one partner has reached the Regelaltersgrenze.

Proposed fix

The Regelaltersgrenze already exists in the pension namespace as sozialversicherung__rente__altersrente__regelaltersrente__altersgrenze (a per-person float in years). The fix:

Step 1: Introduce a per-person boolean (e.g., hat_regelaltersgrenze_erreicht) computed from alter and the existing regelaltersrente__altersgrenze.

Step 2: Replace the gate in Grundsicherung im Alter (im_alter.py). Instead of requiring volljährige_alle_rentenbezieher_hh, check per person whether hat_regelaltersgrenze_erreicht.

Step 3: Replace the gate in Bürgergeld / ALG 2. Instead of excluding all-retiree households, exclude persons who have reached the Regelaltersgrenze from the Bürgergeld claim. Per SGB II §7 Abs. 1 Satz 1 Nr. 1, only persons below the Regelaltersgrenze are eligible for SGB II. See #1157

Step 4: Replace the gate in Wohngeld analogously.

Step 5: Remove volljährige_alle_rentenbezieher_hh from hh_characteristics.py once no function depends on it.

References

• SGB XII §41 Abs. 1–2: Eligibility for Grundsicherung im Alter requires reaching the Regelaltersgrenze
• SGB VI §235: Regelaltersgrenze definition (birth-year dependent, 65→67)
• SGB II §7 Abs. 1 Satz 1 Nr. 1: SGB II eligibility requires being below the Regelaltersgrenze

Related issues

• Supersedes BUG: Treatment of Bedarfsgemeinschaften with both retirees and unemployed job seekers probably incorrect #703 (together with Implement benefit calculation for gemischte Bedarfsgemeinschaft (mixed SGB II / SGB XII couples) #1157)
• Related to BUG: Several bugs in Grundsicherung im Alter #696, BUG: Defintion of Einstandsgemeinschaften SGB XII #738
• The correct treatment of gemischte Bedarfsgemeinschaften (mixed SGB II / SGB XII couples) is tracked in Implement benefit calculation for gemischte Bedarfsgemeinschaft (mixed SGB II / SGB XII couples) #1157