“Forever Young” (1992) is like a labradoodle. It’s a harmlessly cute cross-breed (the result of mating romantic comedy with science fiction). What’s amazing is how easily this film could have become mutant offspring. You’ve got Mel Gibson as a 1939 test pilot who agrees to get cryogenically frozen after his girlfriend falls into a coma, then gets accidentally thawed out after he’d been accidentally forgotten for 50 years. Hijinks ensue: culture shock, military conspiracies, awkward romance, etc. Thankfully, every time the plot could have crashed and burned, the filmmakers pull back on the throttle, so to speak. “Forever Young.” Labradoodle.