Your arms might not be flabby due to aging, but huge weight loss can also stretch the skin to give the same effects of aging, which may or may not be reversible, depending on the elasticity of your skin. (Congratulations by the way, 100+ pounds is GREAT!!!) Since you are young, that is a plus. You might know this, but I want to clarify something for you because I want to make sure that one line you used wasn't just casual terminology. You said you needed to put some tone into the fat. Skin, fat and muscle are all different tissues and you can't convert anything to another tissue, but you can increase your muscle size to replace the empty space where your former fat was. You may not be able to firm the arms up completely with weights, but this can sure put some muscle back in to that empty space.
Lipo also won't make the flab go away if your skin is stretched. It will 'thin out' the floppy part, but if the skin is still hanging 6 months or so after you lose weight, you might need to consider cosmetic surgery to remove the skin.
You will want to rev up your muscle with bicep (front of upper arms) and tricep (back of upper arms) exercises. You can do those with dumbbells, for about a $10-$20 investment. If you know nothing at all about weights, I suggest buying BFL or BFL for Women. If you aren't interested in the eating plan, you can still do the weights. These books will give you some good exercises to choose from.
You don't want to work out the same muscles two days in a row. It is good to change up your exercises at least every 4-6 weeks because your muscles get used to the same movement and you won't have as effective workouts. If you aren't interested in the books, try Kathy Smith Lift Weights to Lose Weight, or her program at
www.beachbody.com . The Beachbody program was my first full course of weights, ( I tried BFL twice, but had to stop both times due to either an injury or surgery) and it was a great all around intorduction to weights until I moved on to something more advanced.
Good luck!