Santa Claus... haven't you seen Miracle on 34th Street?
There's the real story of St. Nicholas, a man who made toys for children at Christmas. If the door was locked, and there were no shoes outside to hide the gifts, he snuck into the house any old way to deliver the gift. He apparently really did sneak down a chimney at least once.
Letting Santa Claus, Kris Kringle, or St. Nick take all the credit makes Christmas more fun. Sometimes people are embarrassed to give poor gifts, or don't know what to give in return. But 'Santa' can give anything to anyone, and nobody has to keep score.
When a present comes from 'Santa Claus', there is a real person behind it who shares this generous spirit. Whether this person is named Nicholas, or Kringle, or something else, is hard to say.
Stories about reindeer, elves, and so on also have elements of truth. Little people far away do make a lot of our presents, working all year round to get ready for Christmas. Most people never see them, and don't know whether they get paid in milk or money. Real reindeer do pull sleighs, though they 'fly' mostly on the ground.
So I'd say that Santa Claus is real in some ways, and in other ways he's a 'cover story' for real people being generous and playful.
It doesn't hurt to play along with the story, even if you're not sure you believe it anymore.
I am over thirty, and I still enjoy a stocking full of treats on Christmas morning. Now that I am big, I tuck a few extra surprises into each stocking when nobody is looking, to encourage 'Santa' to keep up the hard work.
There is an address in North Pole, Alaska, where you can write to Santa Claus. The ZIP code is 99705. I'd definitely include a stamped return envelope with your address, and maybe a small donation to help feed the elves.
Santa Claus House
101 St. Nicholas Dr.
North Pole, Alaska 99705
North Polar - Santa Claus
P.O. Box 56099
North Pole, Alaska 99705-1099