I have used Arrow Leathercare for a few jackets with very positive results. Replacing the zipper won't be a problem at all.
Lengthening the sleeves is another matter entirely. Replacing the sleeves will be a no go. Matching the leather will be impossible and removing and reattaching sleeves is not trivial.
If you could find someone to do the work, it would probably be less expensive to buy a new jacket.
If the sleeves fit you correctly when you were 18 I would be surprised if they were significantly short now, most men don't grow that much once they reach 18, unless you were a late bloomer.

However, if you gained weight around your torso over the years, that will contribute to the sleeves being shorter than they used to fit. Having more girth will cause the body of the jacket to fit tighter and will draw the sleeves upward as the leather stretches across your back. (I may or may not have some experience in this with jackets that fit very well a few years ago, but less so since I've added pounds.)
How short are the sleeves? How much cuff does the sleeve have? You may be able to have the cuff unfolded and reglued/sewn to give a bit more length. However, you'll likely see the line where the current fold is. The sleeve lining would most likely have to be replaced, but that's a relatively easy fix (in fact, one of the jackets I had Arrow work on was to replace the lining).
Regards,
Indiana Jeff