No, all pets are welcome without any age restriction. Although, it's best to consult with your Vet about the suitability of getting your pet to a mass event before planning the trip, as your Vet and you would understand your pet's requirements best.
No, a printed copy is not necessary. You can just take a screenshot of the tickets in your mail or the confirmation SMS and show that to the on-ground team at the registration desk at the event