Biceps can grow about 0.5" a year, so I wouldn't worry too much about making them appear bigger. Also, the way the bicep attaches to the tendon in the arm (long bellied or short bellied) helps with the "peak". You look to be long bellied (flatter) so genetics could play a part.
That being said, the triceps makes up the most of your arms mass, and you can definitely increase both the size and strength of it. If you don't want to do direct bi/tri work, make sure you are incorporating chinups, pushups, bench press, dips etc.