My sister and an were not very close. Something happened when we were teenagers and we completely lost touch with each other. Admittedly, it was probably my fault. I wish I could go back and take everything I ever said.
Lots of people lose younger siblings. You never think it can happen to you. Consider that I have already lost my father and a very close aunt... my mom's little sister, Sherry.
If you have any quarrel between you and a sibling get it over now. I'm 51 and I'm healthy. My sister had just turned 50 in December. I didn't know how unhealthy she was. Even if you're on the other side of the world, send a note. Send something. Don't wait until that brother or sister dies. I can't do anything now.