I'm probably going to be beat for posting something dumb, but here it goes

When I was a newbie, I saw things like "CHEAPEST DWARF ON THE MARKET!!!" Or "ICE FOR 2 GB!!"

And I would think "wow what a deal!" And blow all my hard earned currency on these 14 year old lions. I then would be very upset to find them dead a few days later.

Hear me out, a banner when you click on a trade for an elderly or frozen lion warning that that lion can not be bred ect. It will help with falling for tricks for "cheapest!" For newbies and maybe even older players.

The banner could be easily removed, by in checking the box in the settings menu.

Suggestions:

"I think a red banner like the "X number of lions will leave your pride because they are starving to death" is a good idea."

"It is a good idea, maybe a simplier thing than banner though - just display age next to a lion in trade listing?

Like:
Lions & Cubs:
Newly Claimed Lioness (#NUMBER), 3 years, 3 months old

That way, it wont get in the way, and wont even need to be toggleable as it'd just be a small addition. But it will display age right up and prevent newbie mistakes"