It really creeps up on you and takes you by surprise when they reach their milestones that you swear you only just hit yourself yesterday. Its a really earth shattering moment when your sibling turns 18, graduates university or gets their first job, and it dawns on you that one day they wont be a snot-nosed annoying brat anymore, but a snot-nosed annoying adult. Youll always refer to them as your little brother or baby sister, and that will never change, no matter how old they get, and you cant help but be proud of them and their achievements