Today, marketers are using social media because that's where people spend the most time now and it is also cost effective because you can target your ad. But the marketing world has been doing business without social media for centuries now. I am 34, and even I worked as a marketer before social media.
For reaching a group that opt-out of social media, you should use golden age marketing techniques. You should understand the demographics of your target group and what they do with their lives. Maybe they go to similar events, maybe they read similar magazines, etc.
And don't forget, digital marketing is bigger than social media marketing. Those people still use google, still use other websites. If you make your ads right, they will click it knowing they are clicking an ad. And, you shouldn't base your marketing on tricking your customers anyway, so provide value, use content marketing, make a cool product and they will come.