I'm running a game set in the Hibernian tribunal and a character is joining the covenant who is immune to iron weapons. I know arrowheads can be made from Stone, Bone, Antler, and even lacquered wood, but I'm not sure how common that should be? Should most all arrows fired my 13th century men be tipped with iron? Thanks for any help
Most, but by no means all, arrows fired in the 13th century were tipped with steel which may be different from "iron" depending on how you interpret "iron". Apparently ancient flint arrowheads were called "elf-shot" at the time 
There are also the balls of glue to catch birds with, and there are quite some stone firing crossbows. When exactly is this?
current year is 1221, but the campaign may run for 100 years.
Javelins (quite a few with fire-hardened points) and slings were also quite common, so you can have him be affected by missiles quite easily if he goes to combat too recklessly. THe character will be aware of this, so I would not try to pull a fast one on the player using that.
According to my source most arrowheads in 13th Century Western Europe will be a highly impure steel. (Elton - Arms and Armour 1976 3rd Ed 1988)
Bronze blades which are rare as are Bone Daggers are not Iron. an unshod Quaterstaff is quite common and in the right hands pretty damn lethal.
Andrew
Steel is an alloy of iron, carbon (usually, between 0.2% and 2.1% of weight), and possibly other elements (depending on the type of steel). Interestingly, an alloy of iron and carbon with too much carbon in the mix (between 2.1% and 4%) is called cast iron. For that reason, among other, I would tend to let steel weapon be included in 'iron' weapons.
I'm also pretty sure most arrows fired in the 13th century will be tipped with some form of iron (normally steel), it doesn't take much and it is by then widely available. Of course, once someone decides he needs a non-iron arrow, it will be easy to make; most archers probably know at least the basis of making arrows.
they may have also used obsidian arrow heads as well.
Rare but yes, in areas with easy access it was used for a long time. OTOH, this can be included under "stone"...