Hi there! I can relate with you; I was interested in tornadoes from a very early age as well.
Back in the '60s, the Chicago area "tornado expert" was a TV weatherman named Harry Volkman. Volkman would visit all of the area schools around tornado season, and give talks on tornadoes and severe weather. I never missed a single one.
Today the undisputed severe weather guru in the Chicago area is Tom Skilling. Tom holds annual severe weather seminars at Fermilab in Batavia, IL. I met Tom through other channels, and know that he's always willing to give some time to people like you. You can contact him at WGN-TV in Chicago.
AFAIK there are no hard and fast age limits for storm spotters. If you prove yourself to be reliable, available and serious about storm spotting, you stand a good chance of being included on the roster of official storm spotters in your area, and being allowed to call that secret phone number to report severe weather if you spot it.
As for tips, remember that your training should be an ongoing thing. After going through NOAA/NWS SKYWARN® training, you should keep current with other local storm spotters, refresh your training annually, and look for more advanced training. FEMA has an independent study program that you can take over the Internet. You can even get college credit for some of these courses.
FEMA ISPTry to get involved in local, county and state ESDA programs. Most of these have requirements that will keep you out until you're at least 16 (and can drive), and most probably until you're 18. You also need to be physically fit, and pass a background check. These days, all volunteer organizations, public and private, are governed by the Department of Homeland Security. You must be a US native citizen, have no criminal record, and have no "suspicious" social relationships.
Good luck, and happy hunting!