Apple Pencil life span Recently I bought Apple Pencil (1 with lightning charger) for my iPad Air 3. My question is relating to the life span of this pencil.   I use it about 5 hour a day usually.
Do we know how many years I could expect my pencil to work?
The pencil should last several years if you're careful with it. The two ways it will fail are physical damage and eventual consumption of the batteries. One way you won’t get long life out of a pencil is if you don’t use it and keep it charged monthly.

Avoid hard drops to the hard floor.
Avoid never charging it or letting the battery go totally flat

Things you can fix are overuse, the tips wear out in a year or so of moderate to heavy use. Apple sells replacement tips for your pencil at 4 tips for $19.  Apple also offers battery service for $30.
This link will describe how to tell if tip is worn. You may want to check it out.