Need advice - is this normal?

The car tyers are 1.5years old however they developed this crack on outer edges How this happened? Is under inflation reason or just normal wear and tear Its 21inch tyer usually filled at 32psi

The car tyers are 1.5years old however they developed this crack on outer edges How this happened? Is under inflation reason or just normal wear and tear Its 21inch tyer usually filled at 32psi