turns out: btype->age is never used.

src/kernel/building.h

@@ -70,7 +70,6 @@ extern "C" {
 
         const char *(*name) (const struct building_type *,
             const struct building * b, int size);
-        void(*age) (struct building *);
         double(*taxes) (const struct building *, int level);
         struct attrib *attribs;
     } building_type;

src/kernel/building.test.c

@@ -296,7 +296,6 @@ static void test_btype_defaults(CuTest *tc) {
     CuAssertPtrEquals(tc, 0, btype->maintenance);
     CuAssertPtrEquals(tc, 0, btype->construction);
     CuAssertTrue(tc, !btype->name);
-    CuAssertTrue(tc, !btype->age);
     CuAssertTrue(tc, !btype->taxes);
     CuAssertDblEquals(tc, 1.0, btype->auraregen, 0.0);
     CuAssertIntEquals(tc, -1, btype->maxsize);

src/kernel/xmlreader.c

@@ -369,9 +369,6 @@ static int parse_buildings(xmlDocPtr doc)
                         (const char *(*)(const struct building_type *,
                         const struct building *, int))fun;
                 }
-                else if (strcmp((const char *)propValue, "age") == 0) {
-                    btype->age = (void(*)(struct building *))fun;
-                }
                 else if (strcmp((const char *)propValue, "taxes") == 0) {
                     btype->taxes = (double(*)(const struct building *, int))fun;
                 }

src/laws.c

@@ -2883,10 +2883,6 @@ static building *age_building(building * b)
     a_age(&b->attribs, b);
     handle_event(b->attribs, "timer", b);
 
-    if (b->type->age) {
-        b->type->age(b);
-    }
-
     return b;
 }