I bet that graph is U-shaped of % of people that answer unknown messages vs. age. Kids want to be social, and old people don't know any better. With salty Gen-Xers in the middle.
99.99% of the time I let it go to voicemail. I have since the days of cassette-tape answering machines. The only time I don't is if some just texted and said they are calling. Even when my insurance company hold line asks if I want a callback, I'm too paranoid that a scammer could have infiltrated the callback process.