If “looking at or appreciating” the attractiveness falls into the category of unwanted attention, that’s what makes it creepy or pervy, regardless of age or age differences. If you’re oogling someone much younger, who isn’t interested & doesn’t like dating older people, or worse, a minor, then it’s to be expected that they’ll be even less receptive to the idea. Regardless, it boils down to how the “admiring” is being done, and it’s up to the recipient of that attention to decide how they feel about it, not the one doing the looking, and no matter how polite they may feel they were being.