Dynamic Template file for subpage

The taxonomy term should helps you, see the documentation.

The possibilities

  • taxonomy-{taxonomy}-{term}.php
  • taxonomy-{taxonomy}.php
  • tag-{slug}.php
  • tag-{id}.php

Your example

  • tag-about.php

See the template hierarchy for tag for a deeper documentation about this feature. So it is possible to have a specific template without coding, a plugin.