Shelties do not become fully mature until they are 3-5 years of age. (10/14) by Heather Vance October 22, 2020, 7:54 am Credit Heather Vance 0 Previous 10/14 Next View full list See more Previous article Shelties are a breed that varies more than most others in size. Next article Shetland Sheepdog can be kept both in the apartments and in the houses with backyards. Leave a Reply Cancel replyYour email address will not be published. Required fields are marked *Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment.