Sometimes, it helps to zoom out in your life planning and get a look at long-term family milestones. This timeline spreadsheet gives you a quick overview of important moments.
For me, the key to this timeline is simplicity, so there's not a lot of detailed information recorded there. I have other systems for planning details, but a simple chart like this has proven useful over the years, since it really puts those big moments you want to plan for in perspective. It's also fun to see what ages people will be over the years.
Of course, you should put any information into it that would be helpful to you. This one is just a sample template I put together in Google Docs, and you're more than welcome to grab it if you find it useful.