The can can be recycled if it has been emptied and is not rusty.
Paint
Paint can, Paint container
Recyclable?
Blue Bins & Chutes
Other Recycling
Recommended
Trash
Do not put it in the trash when it is still liquid. Open the top, let it dry out and harden before putting in the trash.
Never pour paint down the drain. Keep leftover paint for touch-ups or dispose of it per instructions above.
Alternative
Freecycle / Give Away
Occasionally there are art projects including mural projects where paint donations are welcome. Likewise others may benefit from you giving your excess paint away.
Art Don't Throw
GoodHood
Olio
Alternative
Tips & Suggestions
Linseed oil aka flax seed can thin the consistency of oil based paint, making it smoother and easier. This might help make some of your slightly older paint more usable.