Your vet could probably estimate it for you. When I adopted Raisin they based him on 3-4 months of age because of his size but he had already had some his adult teeth come in so the vet said he was really arnd 7-8 months. I am sure someone on here has way more experience, hope someone can give you a more precise answer than mine.
P.S. your pup is adorable, love the pic in his “cone of shame”.