Get EntityItem true age

I am trying to make myself an overlay to show how much time I have to pick up items before they despawns.

I found I can get the max amount of time in

EntityItem item // = myItem
item.lifespan

And then assumed it would be easy to find my value :

time_left_for_pickup = String.format("%d", (item.lifespan - item.ticksExisted) / 20 /*ticks per second*/);

But this value starts at 0 every time the item enters my render distance. I also found

item.getAge()

but even this starts at 0 every time the item gets loaded. So I always have a countdown from 5 minutes, but it isn't anyhow helpful because I can't know what the actual age of the item is, I can just show how long the item has been in render distance.

Can I even get this information clientside? Or the true age of an item is reserved for the server?

Edit : I'm testing on a Multiplayer server and on Minecraft 1.12.2 (with Forge 14.23.5.2847), but my mod is completely clientside

Thanks for reading

Edited June 13, 20205 yr by Alunduyn