A Personalized Milestone Birthday Invitation. Choose your background color and add the age to this invitation to let everyone know this is a huge milestone! Personalize! Capture the personality of the celebrant with a greeting or message specific to them. Sizing: Standard invitations are 5″ x 7″. Our graphic artists work their magic on each invitation to create the best invitation possible. Envelopes are included with every order. Proofs: You will receive a proof of your order by email within 2 business days.