I need alittle help with a young longbow maybe you guys can give me some ideas. First what would be a good size/draw weight for a 13 year old 100lb 5"5 boy? Second what are good youth arrows for hunting/general shooting?, Last where is a good place to pick up a good/fair priced youth bow instock?

Chuck at Two Tracks a sponsor here makes some nice ones.
His phone is 989 834 0588

Mike at Maddog Traditional Archery makes a some nice bow for kids and adults at a real value price.  I've got a Maddog Mutt that is a sweet shooter. Check the sponsors links.

Mike@ Maddog
X2

I had JD Berry built my son an Argos longbow (not listed on his website).  That turned out to be good for him to shoot.  It was a 36#@26, 66".  The idea is if the weight is too light for him going forward, we can have James make the limbs shorter to increase the weight.

By 13 he is already developing arm strength and can likely pull 40-45# and has a draw around 25", which would translate to a 50# adult bow approx-get him to shoot some bows like that-as many as you can and get him something off the classifieds.
Adult arrows too......just leave them long if you need to for proper tuning. At that age I got my son an ACS CX-50#@28, which he is still shooting and hunting with at 17, and does not even want to hear about another bow.

Maddog or Black Rhino. My son is 13, 100# and shoots 45# at his 25" draw.

Also you could look into any of the sponsers who sell a 3 piece takedown. A friend of mine did this for his son and just bought new, heavier limbs as his son aged and got stronger.

My 14 yr old is about that same size and he is shooting a 58" Crow Creek Copperhead that is 48 @ 28.  I'm not sure of his draw length but I would guess it to be around 25"  He is shooting Beeman MFX Classics with 100 grain inserts and 220 gr Muzzy Phantoms 28" long.  They fly like darts and he is pretty darn accurate with this set-up!  If a deer comes within 10-12 yards it's gonna have a bad day!

Look at the youth bows at 3-Rivers.  They are very well made and won't break the bank.  They have everything you will need, bow, arrows, arm guard, tab or glove, quiver.  I give bows to kids from age 10 to 20, a first bow should be real light, 20-30 pounds, so he is not fighting the bow while he is learning proper form.  If they stick with it, you can get them a stronger bow six months to a year later.  Bill

Another vote for Maddog!!

Starting out for that small of a kids I would suggest 30-35@ 28. Most likely he will only draw about 24-25 inches.

I also suggest Maddog for a new one.

James