Luffy will grow, m8.
That's how One Piece weird ass sizes work.
And what if she's older?
Luffy is gonna die young anyway, since it's been said time and time again in the story that he's constantly shortening his lifespan.
And if Hancock keep the looks like Shakky.....well....I can guarantee that these 10 years difference won't mean shit.
There was another guy called Nico and Pancho, he had the most adorable chihuahua that he made videos with, he really loved and bonded with that dog. My heart completely broke when not long after he was mauled by another dog he died due to someone else instead too, he always had problems with heart murmurs or such too. His owner really loved that dog and it was heartbreaking to see him come to terms with losing him.
I watched my pets get killed and die as a child so I'm no stranger to seeing pets die either but it fucks you up for real, I can't even imagine how it feels for these people who knew their pets for so long, when I knew mine a fraction of the time at best and it fucked up me to this day too:
My aunts pet dog, one of her 4 dogs, a mother dog was like my first best friend, my closest and most caring "person" or figure in my life at that time too. I didn't have to see her die as I moved away to the UK before she passed away but saying goodbye to her and never seeing her again, hurt me in way I never recovered from either.