A nice simple notification popup, 'Birthday' whenever a colonist ages 1 year would be great for RP and as a better indicator of time, especially for smaller colonies.
You can already get them periodically, but it seems only when it is also acompanied by an age related disease like Artery Blockage. :'(
I think you would enjoy the Days Matter mod. It's steam only and not updated for 1.0 yet, but I hope there will be an update soon.