The 12.6V number means the battery doesn't have any shorted cells. Good.12.6V resting
14.6 with engine running.
The 14.6V number means the charging system is doing its thing. Good.
Now, the next test is to measure the battery voltage while the engine is being cranked. Much lower than 9.0V and I'd suspect a weak battery. Seems early to be worn out but this does sometimes happen. Also check the battery and chassis ground connections for corrosion.
As the man ^^ says, a car repair facility can check the battery under load (the only true test of a battery).