You know people can just not use their real names. E.g Ace. He went by Portgas D. Ace and not Gol D. Ace. Dragon's name may be Rocks D. Dragon but he decided to use Monkey D after marrying Garp's daughter hide the truth(Not actually true, I'm answering as if the theory was proven to be true)

That's why I said kinda adopted.. I wasn't sure if Whitebeard actually tried to adopt Ace or just considered each other as family(maybe in One Piece, that's already considered adoption)

Ace and Luffy venturing out at 17 has nothing to do with Dragon being adopted at 17. Its just a theory based on me thinking that Dragon and Rocks look similar. I don't know if there's any reason that he would adopt, I just said he could've adopted.

No need to write so many comments in a row, it reminds me of a user that was here some time ago.

Anyway, looks don't mean much, a son can look similar to a parent just like they can look completely different. Garp was also in his 20's when Dragon was born so it makes sense for Dragon to be his biological son. Dragon has also been stated to be Garp's son anyway, had that not been the case Oda would have said so, for example, Ace was said to be Luffy's brother but it was never said that he was Garp's grandson.

Sorry lol ,I just realized I could edit comments since I'm not usually on here.

Also, Dragon has been stated to have been Garp's son but maybe they also didn't know the truth( Not actually the truth but you get what I mean). Maybe Garp took him in secretly so even people like Sengoku who knows and probably participated in the God-Valley War didn't know.

Also, sons (or children in general)usually look similar to their dads/parents but then again, it's One Piece, Big Mom doesn't exactly look like Katakuri and same for Yamato and Kaido

Sengoku and Garp seemed to be pretty good friends and went up through the ranks together, similar to how Sakazuki and Borsalino are now. I'm sure Sengoku would know if Dragon was "adopted"

I don't know, maybe he kept a it secret from Sengoku, I mean friends(and best friends) do keep secrets from each other but Sengoku could have known but chose to keep it a secret, maybe he's saving it for the time when they capture Dragon(Like in Marineford, he revealed who Luffy and Ace are actually related to it he has known it for a long time since he's friends with Garp) ,I don't know. I'm just making stuff up at this point since I didn't exactly think about everyone else. I'm the average One Piece Theorist , just kidding lol

He told Sengoku he was raising the pirate king's son (that's the only way he would know Ace's identity) Dragon being his son is nowhere near that bad so why keep it a secret? Anyway, it's all good

I'd say it is as bad since Rocks and the Rocks Pirates took both Garp and Roger to defeat. Maybe Sengoku is just being cheeky and once they capture Dragon, he's gonna reveal that he is Rock's son just like how he didn't tell the world that Luffy is related to Garp and Dragon and that Ace and Roger are related until Marineford War

I think Blackbeard is Rocks son. That's how he knew Whitebeard well enough to join his crew. This also fits better with the themes in One Piece.