From soon after Kittyhawk into the 60s and 70s military aircraft advanced by successive models, each going from entering to leaving front-line service in a decade or less. Starting in the late 50s and becoming the norm from the 70s onward, platforms came into service that were flexible enough to stay in service through successive generations of upgrades. So, yeah. The B-52, B-1, A-10, F-15, F-16, F-18, C-130, C-5, etc. platforms are old, but their current models are much more capable than the versions that first entered service.