It is never too late to start!
I'd say only 25% of our cats came to us as kittens, under 6mo old. The other 25% came to us between 6-18mo old. But, the majority (50%) of our cats have come to us as adults between the ages of 2 and 9 years old, and most of them feral. The 9yr old was a feral tomcat, btw. He turned out to be one of our coolest housecats, evah!
Say their name, look at their eyes and smile at them when/if they look at you when you say their name. When you speak with them, pet them, interact in any way, say their name or call them by name as much as you can. When they look at you when you say their name, praise them, and maybe walk over and love on them (pet, stroke, scrubble, scratch, rub...whatever they like) and/or give them a treat. Eventually, you can try calling them to you (by name) and when they come, give them a treat. Bribery, I know, but it works.
LuckyDuck will fetch a favorite stuffed mouse/mole toy for me to throw over and over down the hall or on the bed. He also wags his tail. His tail is always moving, it is only still when he sleeps. Shadow will also wag her tail back/forth when you pet or scrubble her. Usually a waving (wagging side-to-side) tail on a cat means they are angry or aggresive. Some cats are just special and they do it when they feel good.