Video:
I maked a not listed Video (01:30s, english, with subtitle):
https://youtu.be/MGtb2zOQdYM
Please watch this because thats the best explanation.
Text:
When you want to detect the AGE value of an dropped item, there is no problem, BUT when you drop the Item from your Inventory (E and drag it out of it) THERE ISNT A AGE!
I detected this while MapMaking.
Watch my Video of the Bug, its better than a text!
Comments 2
Because you check for age 100 but the item starts at 4800 when dropped from inventory, you could either check at age 4900 (4800+100) in another command block, or use this solution with scoreboards:
Do this command one time to set up: /scoreboard objectives add age dummy
Do this every tick: scoreboard players add @e[type=Item] age 1
Then replace your age testing command with: scoreboard players tag @e[type=Item,score_age_min=100] add old
PS: I'm assuming that 4800 is the correct age of items dropped from the inventory, but it's probably better to do the scoreboard way to be sure.
I can see a Age tag in said item just fine, it starts at a value of about 4800, unlike q dropped, which starts at 0.