(For full clarity, everyone is of age in these scenarios, and frankly you could be well into your 30s and still have quite a gap with the Papas so keep that in mind)
With Copia, it's not a factor from the start. You only figure it out once you've been seeing each other for a while, when you're teasing him about your age difference. It was just playful, maybe a comment on his movie tastes, his video games, a new strand of gray in his hair. It's not meant to be salacious in any way, just a bit of fun.
But you can recognize the way his spine stiffens, how his eyes dilate. That night is the first time you get to see him really take control. It's exhilarating for him, just like when you use his title, another way to hold power over someone when he'd never had any control in his life before. He's rougher than normal, but the same anxious mess with aftercare as always, if not more so, afraid he may have overstepped. It's only when you assure him you're into it too that he's able to fully relax again.
Secondo has been very clear about how he feels about your age gap from the beginning - while it's not the primary reason for his attraction to you, it certainly has been and is a factor. He's more experienced, wiser, and getting to teach you things - both inside and out of the bedroom - brings him a little thrill. He gets to show you so much of the world, and no matter how experienced you are, he's more knowledgeable in nearly every way.
And you play it up too, mostly to be a brat, which he certainly has fun with as well. All you have to do is call him "old man" in the wrong tone of voice and you know you'll be feeling it in the morning, just like the both of you wanted. (Also definitely has a Daddy kink like, come on.)
For Terzo, it's not explicitly because he's older than you, but more as part of his corruption kink. If you pointed out his age directly, he might actually be insulted - Terzo is not old and he will absolutely remind you of that as often as he needs to - but it does play into the power dynamic between you. He outranks you, he's more knowledgeable than you, and you're just so sweet and perfect. Tender and young and inexperienced, he wants to show you the world.
He also wants to see how far he can push you (within reason, of course, he's not a monster). And you like learning from him, like seeing the darker side of things, pushing the limits. Having such a vivacious teacher is certainly a bonus, and with all his experience he can absolutely show you a good time.
Primo is also into expanding your horizons, but it's far more equal than his younger brothers. You are young, yes, and maybe even a little naive, but that just means you need someone to protect you. To watch over you and guide you, always taking your cue which path you'd like to walk down. Watching you experience things for the first time makes him feel young again.
The most you'll get out of him as a direct confirmation he likes that you're younger is the way he reacts when others point out the gap - his face might flush under his paints, his grip on you might tighten slightly. Sometimes he worries he won't be enough for you, that you'll find someone closer to your age, someone who's more spry and flexible (figuratively and literally), but you always reassure him he's more than enough.
Nihil is absolutely delusional and still sees himself as a 50 year old hot-shot when his body isn't inconvenient enough to remind him he is not, so he actually doesn't really think about the age gap between you two much - despite it being the largest out of the group! But he'd love you even if you were (somehow) older than him, as far as he's concerned the sun shines just for you, so it doesn't matter that he's robbing the cradle - you're all his.