How big will my arms be.?

Hey. I am 13 years and 10.5 months old. I usually work out naturally, and go to the gym sometimes with mey friends. At almost 14 years old now, my arm diameter while flexing is 13 inches. I am getting bicep curls, and additional arm workout weights tommorow. Do you think i have big arms now, like average? And, if i constantly remain dedicated and workout oftenly, do you think my arms will be large as an adult. How big? Thanks!