I'm 29, and interested in literature, music (primarily classical music and jazz), history, and to some extent in art. Feel free to write about anything in postcards you send me, though.
Cards I am interested in receiving:
Old, interesting or unusual buildings and architecture
Landscapes and cityscapes
Vintage cards , especially if they relate to one of my other interests in some way
Graveyards/cemeteries (real ones)
Statues and sculptures, and museum-style paintings or artwork
In general, I like photographs better than drawings except when the card is of some painting that could be in a museum. Some drawings that aren't museum style art are good but the paintings are more what I'm looking for if it isn't a photograph.
If you do not have any cards that fit into the above categories, that is fine and you can send a nice card out of what you have available - the above list is just what I usually like the most.
I don't favorite cards nearly as often as I used to, but it is fairly representative of what I like. Don't be offended if I don't add your cards to my favorites list - I get cards I like all the time and figured if I kept favoriting them, it would just show a lot of my most recently received cards, haha.