How can I define my abs and arms more?

You will probably think I am kidding, but i am not: Scrub the walls and ceilings in your home. If you want to tone and build your arms and abs, you need some long term low impact hardening of those muscles, and the couple days it takes to scrub your walls and ceilings really well will do that. Your mom will also love you :) Envision the Karate Kid movie: Wax on, Wax off...

Jobs such as painting will also do it... something that keeps your arms up in front of you and moving: Trimming hedges, waiting tables in a place where they use large trays (be sure and switch arms) (and not eat too much).

If you have never done manual labor you will not hold upper body tone or bulk, and though sports like tennis or swimming will put it on, it will not KEEP it on, because you do not do those things for uninterrupted low impact HOURS.

My skinny 17yo son gained 30 pounds and put on an 8 pack and a gorgeous set of shoulders running a grinder on ships in about a month. My older son still has his from the same period of HIS life 5 years ago :) After you have scrubbed your house, you will not embarrassingly DIE doing other work of this 'arms up' type, they even PAY you for it ;) Go for it.

protein shakes are always good for any advance muscle growing. you should eat meats with proteins and lots of fruits and vegetables, also you should do sit-ups and push-ups even though they are old school they still work!