I'm sure the range of praise has been exhausted, but I really don't care - I'm going to tell you how touching and beautiful this story is, and then I'm going to stomp around until there is a wealth of established relationship/ageing/life-long love Snarry fics for me to enjoy as much as I did this wonderful piece.
I'm a hopeless romantic, but I also grew up with seniors(my mom's a gerontologist.), so I've also seen what the passage of time looks like on many different people. I loved the reality of ageing as seen through the wizarding care text, as well as through Harry's eyes and the eyes of his children. I loved Harry's fierce defence of his bond with Severus and the importance of the blessing passed down through the generations.
I'm sorry it took me so long to find some time today to read this.
Well done, sweetie! (and I really wish I could vote! heh)