You are out by a few dozen orders of magnitude. If you were to build a computer which could churn out 1 trillion seed phrases a second, then you are looking at somewhere around 10 billion billion years to exhaust an 128 bit search space. Increase that to 256 bits, and the numbers become comical.

In short, to answer OP's original question: Yes, it is theoretically possible for your wallet to generate an already used address, but our sun will have engulfed the Earth long before that ever happens.