I currently have two cats, one is definitely older than the other and by all rights should be terrified of absolutely everything. Male orange tabby, he was a stray we took in during hurricane season about 7 years ago. He has right hip damage that suggests he was either kicked or hit by something as a young cat and it was never properly set so healed 'off'. He is afraid of shoes, shirts, feet, noises (laughter has been known to send him running), his own body noises (he once farted in his sleep, loud enough that it won't him up and sent him tearing through the house, crashing into things, before finally hiding under the bed for about 6 hours), rain, people, etc. This is a cat that for the first three years we had him, would pee in the closet if strange people came into the house just so that he wouldn't have to go downstairs to use his litter box.
Then we ended up getting a calico female from the shelter. She's probably 3-4 years younger than him, has asthma, and is very loving and active. She makes strange noises often (wheezing from her asthma) that by all right SHOULD send the older cat into flee mode. However, instead, she has slowly but surely helped to socialize him. He's still skittish (probably always will be), but he no longer jumps at shadows or his own noises, and he'll even sit with us and purr these days. I can change my shirt and not have him act like the world is ending. He's even joining the morning cacophony for breakfast and lets us know when the food dish is less than full!
Sometimes a scared cat is a scared cat... but sometimes having another cat can help them mellow out.