Sad. Alzheimer's is one of those that takes your loved one before death does, and it's heart-wrenching. I watched my grandmother go through it, and I watched what that process did to my aunts, my uncles, and my mom.
Friend of mine from college is kid 12 out of 13. Her dad was over 70 by the time she got to college, and didn't live much longer after. She loved her parents dearly, but has commented that having parents who were markedly older did rip her off in a few ways. She didn't get to know them for as long, she didn't get to horse around or rough-house with them the way little kids do with their parents, and their time was always divided. My friend got the short end of TWO sticks, really: they were old, and she was youngest in a huge brood. Could be why the aforementioned friend had exactly ONE kid, and is making sure he gets to get out in nature and see lots of different places (two things her parents never did due to age and lack of money).
When you make decisions, there's always a tradeoff. People who breed late can do their kids a massive disservice.