AES always has a 128 bit (16 byte) block size; AES-256, AES-192 and AES-128 only...

AES always has a 128 bit (16 byte) block size; AES-256, AES-192 and AES-128 only change the key size.

(Also, the 128-byte buffer therefore contains 8 blocks; I believe the size is chosen more for performance than security reasons.)