Usually? Since when? The YF-16 first flew in 1974. The first production F-16A flew in 1976. It took four years before it entered operational service in 1980 with the 34th Tactical Fighter Squadron, 388th Tactical Fighter Wing. However it still had lots of temporary operational limits due to a number of problems and limited to only Sidewinders in the A2A role. In 1980 seven F-16A's crashed due to a number of engine and avionics related problems. In 1981, 15 F-16's crashed. The whole fleet was grounded several times. It wasn't until the F-16C/D Block 25 upgrade in 1984 that the full A2A potential was reached with the ability to carry radar guided missiles. It took ten years from first flight to a mature weapon system. The F-35A first flew in December 2006, nine years ago, and it is a helluva lot more complex weapon system than the F-16 was back then.