First of all we already have topic thumbnails you can enable it from the ACP.
If that isn't enough you can take a look at the code that makes it work and duplicate that.
The birthdate field looks like it wants
However, it's not possible to type dashes, and using the date selector fills in using
mm/dd/yyyy format. My age shows correctly in my profile, so I guess the placeholder text is just outdated.
Also in the topic listing, I move my mouse to the left white space so I can read the topic names, but it crosses over an avatar temporarily and suddenly a usercard is permanently obscuring topic names, and I have to move my mouse all over the place until it goes away (it stays forever if I leave my mouse in the white area on the left)