Do not decide from age alone
Equipment age is context, not a diagnosis. Start with the failed component, overall condition, and whether the system has a pattern of recurring problems.
Consider comfort and performance
Uneven cooling, persistent humidity or airflow issues, and inability to maintain temperature can be relevant if they are tied to the system rather than a separate duct or home-envelope issue.
Get the scope in writing
For either path, understand what work is included and what assumptions the recommendation depends on.
Safety note: If you smell gas, see smoke or fire, suspect carbon monoxide, or believe there is an immediate safety danger, leave the area as appropriate and contact the relevant emergency or utility service. Do not treat an active safety emergency as a routine HVAC appointment.