Is my workout plan good? If not, what should I do that is better for me?

I think that it is necessary to state that I am 13. I do the following arm workouts every 2 days. 3 sets of 20 forearm lifts with 5 pound weights. 3 sets of 20 bicep lifts in front of me and at my sides with 5 pound weights. 3 sets of 15 tricep lifts from my back and over my head with 3 pound weights. I've been doing the weight lifts for about 3 months and I had a period of about 2 or 3 weeks without doing any. I have recently starting doing as many pull-ups as I can, sit-ups, planks, running in place thing for 30 seconds, and crunches. I shuffle between those for a few minutes. I am not completely sure if this is what I should doing, and I do those about 3 times in a week. I also have a pull-up bar setup, I use that every once in a while and I'm pretty bad at it.