First of all we already have topic thumbnails you can enable it from the ACP.
upload-8a9aca4d-0f16-435e-a1de-8789d27056c7
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 yyyy-mm-dd
format:
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 My age shows correctly in my profile, so I guess the placeholder text is just outdated.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)
Mm, the user cards are new, so it could probably use some polish.
Ping @psychobunny
The bday thing, @baris