When I was first diagnosed, my appetite had dropped to nothing. I lost more than 50 lbs in about a month. It sounds cool on paper but that kind of weight loss can kill you.
I highly recommend you keep eating, even with the discomfort. A while back, I was having a particularly bad flare, and my appetite dropped significantly. I was feeling a little woozy and light headed. I was taking a shower when finally the hunger, light-headedness and heat of the shower combined to drop me like a rock. I lost consciousness, and on the way down to the floor, my back found the faucet. It took me a month of working with the chiropractor to get to the point where I could walk around without pain, and it still twinges every now and then... I suspect it always will.
Such rapid weight loss is dangerous. You need to keep eating. I know how uncomfortable it is, but trust me, in the long run it's worth it. One of the things that helps when I'm having a flare is to eat lots and lots of mozzarella cheese. I usually melt it over spaghetti, or make a quesadilla.
anyway, as for your question, I was diagnosed over christmas break of my junior year in high school. i think. idk, its been a long time, i forget the exact year. anyway, i hadnt been feeling well all month, was having bad diarrhea, no appetite. like i said, i lost 50+ lbs. I still thought I was just having a bad case if D, but my parents noticed the weight loss and took me to the doctor. She ran a few tests, said she thought it could be Crohn's, and sent me over to Mayo Clinic for confirmation. They did some bloodwork, a colonoscopy, and that was that. I officially had Crohn's. Took maybe a week from the first visit to the diagnosis, three or so from first symptoms. I'm lucky, though. I live a mere 20 miles from Mayo's main campus.
21, Male, diagnosed over Christmas Break of my Junior year in High School.