Is pastel a bit too childish ?
There doesn't have to be unicorns everywhere, it's fine ! Even adults can have a bit of sweetness. So if it's your 20th, and you dream of a sweet vibe, do it. And even if its your 60th and you want aparty that takes you back to your childhood, that's okay too ! Create a candy bar or a sweet table covered in marshmallows and other sweets. Go for a decor backdrop of pastel balloons and why not even a ballon wall to set up for a photobooth with friends.
And can adults have a pinata ?
Of course. If children carefully pull on the strings of a pinata, you're allowed to attack it with a brrom handle and destroy it as you should according to tradition. Fill it with sweet treats, confetti, gifts for your guests like unique glasses, super cool badges and great key chains !