Looking at a 2023 Mazda CX9 Carbon Edition Certified Pre Owned. The dealer sent me the Auto Check and it shows that the first oil service was not done until 8900 miles. It seems to have had regular oil changes since and now has 20,000 miles. Should I have any concerns buying the car as the first oil change was not done until almost 9000 miles?

 

No concern at all. Mazda recommended change is 7500 miles or one year. 8900 miles is no big deal.
"According to the scheduled maintenance section of the owner's manual, the service interval specification for changing the motor oil and oil filter is every 7,500 miles (12,000 km) or at least once a year. Most owners will use the "flexible maintenance interval" as indicated by the oil life meter on the "maintenance monitor" system and change the oil when the "wrench" indicator light is displayed on the gauge cluster."

 

You should be able to easily get 10K miles with synthetic and the factory filled it with 5w-30 synthetic anyways. Good luck.

 

Quite a while ago I worked with a guy at a Mazda distributor who investigated synthetic oil. He found no wear for 15000 miles. Seems like there wouldn't be any damaging wear for semi-synthetic at 8900