the heartwood will be suitable for a bow the longer yew sits the darker the heartwood gets. so 20 yrs?.....should be beautiful dark color.ij got some free yew once....a woodpecker had gotten to it and a couple of of inches under the sapwood was rotten or diseased idk but under that made some excellent bows. i know it sounds like a nightmare, but chase those rings. one stave took me 7 hrs. to chase but dang it was worth it (natives didnt use sapwood so neither will i ), it came out beautiful. shoots like a champ. unbacked heartwood yew is one of my favorites!
and yah throw some sinew cable on there and bam! you got my favorite bow of all time the Inuit bow. fast shooting, excellent cast. with variable draw weights.