fix(mobile): correct person age singular pluralization (#29868)

The ICU plural string for person_age_years in i18n/en.json only defined
the other plural category, so the intl MessageFormat runtime always
fell back to it — displaying '1 years old' instead of '1 year old'.

Added the missing one plural category:

Before: {years, plural, other {# years}} old
After:  {years, plural, one {# year} other {# years}} old

No Dart source changes required. formatAge already uses the
localization system correctly.

Fixes #29865

Co-authored-by: priyanshuANDcoad <priyanshu23154050@akgec.ac.in>

i18n/en.json

@@ -1621,7 +1621,7 @@
   "person": "Person",
   "person_age_months": "{months, plural, one {# month} other {# months}} old",
   "person_age_year_months": "1 year, {months, plural, one {# month} other {# months}} old",
-  "person_age_years": "{years, plural, other {# years}} old",
+  "person_age_years": "{years, plural, one {# year} other {# years}} old",
   "person_birthdate": "Born on {date}",
   "person_hidden": "{name}{hidden, select, true { (hidden)} other {}}",
   "person_recognized": "Person recognized",