What's considered old decoration can depend on the player. I know I started in 2004 and have seen plenty of home decor. It all depends on the year in Tibia but I will mention some in no particular order.
I know back in the day you would see a bunch of crates displayed in houses and on top you would a beloved set. In which most would take off every night and take as needed (guilty, as charged).
It wasn't uncommon in later years to see Magic Plate Armors with Mastermind Shields topped with Giant Spider Silk .
Literally people would throw items in their house and it was still cool and amazing because you would see items that you had no idea how to get or you knew they were super rare at the time.
Houses were more practical in the days, were used mostly for storage or hiding away from creatures etc. Also houses were known for holding celebrations like marriage or Christmas parties! You can say it was just a party everyday in Tibia if you knew someone who owned a house.
Let me mention some items that were popular decoration back in "the day" or my days:
The number one decor: Blood Herbs
Let's not forget about the incredible Atlas
Everyday essentials right in front of the door to mana sit: Dragon Ham , Blank Rune ..other food items as well depending on your taste lol
Gems were quite popular - Talons , Small Diamonds , Scarab Coins .
Quest items - Skull of Ratha , Annihilation Bear Model Ship Firlefanz Goldfish Bowls
Cute items- Doll , Seal Doll , Piggy Banks Stuffed Dragons
Items bought from store (and no not with Tibia Coins) - Cuckoo Clock , Minotaur Statue , Pictures , Wall Mirrors , Tapestries , Cooking items w/ an oven , Pillows , Water Pipes , Bird Cages .... practically anything you can get from the store!
Tusks from Elephants
Footballs (If you were lucky enough to push it to your house back in the day)
What I remember strongly is the house being decorated for marriages. Here's one of me getting married back in the day:
And of my friends marriage sorry for the poor images: