Whoa! I forgot about those scumbags. Let's just say then that the person who eats a DF and gets to experiment with its powers has to be the most knowledgeable person about that specific DF. That's why I didn't want to take what Marco said seriously, and I'm willing to ignore (for the first time) the fact that Oda doesn't include random dialogue lines in his story.
From what I've seen, I don't think that BB would enjoy being immortal. I think that he likes his adventures and enjoys the thrill of risking his life in order to achieve his goals (His face off with Magellan made me think that he is similar to luffy when it comes to recklessness...).
BB is a strong believer in fate and in the dreams of men... I would say that he won't go for immortality even if he knew about it, because it's like cheating fate.
I don't share the same feeling about BB tbh, for the very good reason that he was seen begging for his life so to speak:
So it could be that he was afraid of dying, when he asked WB if he was serious about killing him. He tried to play the son card and strike a sensitive chord so that WB would let him go. So to me it could be that deep down he's afraid of dying, which can be seen as something that makes him different from the rest of the Ds. There are even some who doubt that he's a real D. He's reckless, but he's also someone who was hiding in WB's shadow, and waited years before going along with his plan. So he carefully planned each one of his steps, so I guess that makes him less reckless imo.Maybe even cowardly because of the whole hiding in WB's shadow.
Other than the not dying part which is not confirmed atm, there's the fact that the "ageless surgery" could simply allow him to stay young. Now how can that be interesting to him, during his battle with WB he said that the latter grew old and weak, so to me it could be interesting for BB to have someone perform the ageless surgery on him, so as to not age. This in theory would allow him to stay strong and not become elderly and thus weak.WB was considered the strongest man, but even him grew weak as age took a toll on his health.
It really depends on what the ageless surgery can do. We're not sure if it would allow someone to become literally immortal as in he cannot be killed. But even if it doesn't it could allow him to not age basically, thus keeping his strength as he sits at the apex of the world as the PK. For those reasons I think it could be interesting for BB to get his hands on the Ope Ope.
I think that in the end only a few people know about the ageless surgery. Of course it goes without saying that if BB knew and he was indeed interested he would have already looked for it. We might not know for sure, but it's still a possibility, and it might not happen as it involves Law dying.And I'm not sure if many are ok with that.
I had always like the way Robin responded to Franky when he was in Chopper's body and how Robin warned him to behave while in it. 
She really didn't like "cuteness" to be ruined.
