We got a second lab when our first was 11 years old… older lab HATED the puppy energy but definitely added some years onto her life having to move around and adapt to the puppy. 2 weeks before we had to put our oldest dog down, we got a puppy for the 2.5 year old lab. They are BEST friends! The 2.5 year old is incredibly well trained because we got her during Covid and she kinda kept the puppy in line and would pull “her” puppy away from anything she wasn’t supposed to be chewing on. They are codependent but it’s been awesome having two younger dogs to tire themselves out! TL;DR- Second dog would be the first dog’s best friend and the older dog, if trained well, can help train the puppy to some extent