Parameterize age 35 threshold in LHA shared accommodation rules

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+      - Parameterize age 35 threshold in LHA shared accommodation rules

policyengine_uk/parameters/gov/dwp/LHA/shared_accommodation_age_threshold.yaml

@@ -0,0 +1,12 @@
+description: Age threshold below which single adults without children can only claim shared accommodation rates under LHA
+values:
+  2013-04-01: 35
+metadata:
+  period: year
+  unit: year
+  label: LHA shared accommodation age threshold
+  reference:
+    - title: The Housing Benefit Regulations 2006 - Schedule 4 - Paragraph 28
+      href: https://www.legislation.gov.uk/uksi/2013/376/schedule/4/paragraph/28
+    - title: LHA shared accommodation rate guidance
+      href: https://www.gov.uk/government/publications/local-housing-allowance-rates-applicable-from-april-2013

policyengine_uk/variables/gov/dwp/LHA_category.py

@@ -36,11 +36,13 @@ def formula(benunit, period, parameters):
             household.max(person("age", period))
         )
         has_children = benunit.any(person("is_child", period))
-        # Households with only one adult, if under 35, can only claim shared if without children:
+        # Households with only one adult, if under age threshold, can only
+        # claim shared if without children:
         # https://www.legislation.gov.uk/uksi/2013/376/schedule/4/paragraph/28
+        p = parameters(period).gov.dwp.LHA
         can_only_claim_shared = (
             (num_adults_in_hh == 1)
-            & (eldest_adult_age_in_hh < 35)
+            & (eldest_adult_age_in_hh < p.shared_accommodation_age_threshold)
             & ~has_children
         )
         return select(