You gotta hit the long head, short head and Brachialis. Incling curls with your elbow behind you, some type of curl with your elbows at your side or in front of you like concentration curls, preacher curls etc. And a variation of the hammer curl, either seated or standing. 1 exercise for each head.
Im 60 now and still do heavy construction, this building im on is 30 stories now and our man lift died so i did 500 stories one week. I do this because ive always stayed in shape and from 36 to 46 i hit the bodybuilding hard for the 3rd time in my life getting to 254 pounds with 35 inch thighs, 22+ inch arms and pressed over 500 pounds and in only 5 foot 7 so alot of 3 days on 1 day off and eatting 8000 calories a day, if pro bodybuilders did it so did i and the arm routine above i did many times and it works very well, try it for 12 to 16 weeks then switch up to shock the muscles
1) Incline curl, leaning back on bench at about 45 degrees.
2) Hammer ("beer-mug") curl.
3) Preacher curl.
Make all reps slow, purposeful, and deliberate, maintaining form and resisting gravity both in raising and lowering weight. Weight amount should be taxing, approaching failure point at around the eighth rep in each set.