2007 Subaru Impreza 2.5i

The dealership says I need a catalytic converter because the check engine light is on but it only has 81000 miles. How could this be?

Check your owner’s manual. I think it’s still under warranty.

Actually, the OP needs to check a separate booklet titled, Subaru Maintenance and Warranty Guide.
Yes, it is very possible that this is covered by the Federal Emissions Warranty.

There could also be a misdiagnosis; easy to do when it comes to converters and O2 sensors.
You might post any codes and if this is not known to you drop by an AutoZone or some similar parts house and have the car scanned. They will do this for you free.

It sounds like the dealership want to you to pay as this is slightly out of warranty by 1k miles.

I would contact SOA if this is the case and state how disappointed you are in this with a 4 year old. Be firm but polite.

It is very atypical to change a converter this early on any make.