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>