Are my fears justified or will it get better?

We just rescued a 12 week old pup - we’ve been told he’s presa canario but have a DNA test coming in a couple weeks as he’s part of a dumped litter so we’re not sure.

This guy (Frankie) is a whirlwind. The first week was the worst experience of my life, puppy blues hit HARD. However, after a week of having him, we’ve nailed sit, come, lie down, name recognition, sleeping through the night in his crate, and we’re almost there with toilet training. He’s also doing great on his loose lead walking which is a god send. This may be normal for puppies, but I’m pretty sure he’s a genius.

My concern lies with how big he’s going to get, and how long the puppy behaviour will last with his growing size. When he goes into shark mode where no toy, treat or training will deter him from destroying things or nipping us, I’m at a loss on how to deter him. At 13kg I can still pick him up and put him in air jail or pull him away from something he shouldn’t have.

I’m seeing a lot of how mastiffs can get to 30kg+ at 6 months, and the last puppy I had (not mastiff) was very much still puppy at 1-1.5 years.

Basically/tl;dr - how do you handle massive puppy mastiff?! I’m not a gym buff, I’m just a 30 year old woman who has skipped arm day enough times that I think Frankie is going to rip my arms off in a couple months 😅