We butcher a Longhorn bull every year. We prefer to slaughter between about 12 and 14 months of age and do not put the bull with any females. Have found that if they are kept in a small pasture and fed good grass hay (10% + CP), and slaughter them between 600 and 800 lbs their meat turns out very good. We do not finish on grain, protein cubes or anything...strictly grass fed beef.
Meat does taste differently ( but excellent in our opinion) and doesn't have that "greasy taste" of feedlot grain fed cattle. Meat is very lean. Is best to use an animal that naturally fills out well and doesn't have that "lean, mean, rangy" look. Check our website to see some photos of our cattle and their body condition.
I do not recommend butchering a bull that is in service and has bred females, or one that is over 18 months of age. Meat will be on tougher side, especially if it has a lot of room to run around (large pasture) and exercise. We keep our young bulls (2 or 3 at most) in about a 1/2 acre paddock and only feed them quality hay ("horse" quality or alfalfa). They have enough room to exercise but not enough to get tough. However, if you do butcher an older bull or cow, I'd turn most of it into ground beef (naturally 95 to 98% lean), and use the "best cuts" (tenderloin, ribeye, or sirloin) only for steaks or roasts...then you might have to cook longer with an old animal. The ground meat also makes excellent beef sausage! LH beef cooks fast since there is little fat for insulation against heat. Cook at low to medium temperature, (well done, but not overcooked for ground beef).