Dude. Dude. You were observing and interviewing the population that might be using your product? You've been DOING some UX. Not entirely, but an important part of it. (Think of what Steve Blank calls "customer development".) As "design" == "solving problems", "UX" == "how it does and why it does it", not "how it looks".
Sorry Lawrence, it's a common misapprehension, but you seem to be thinking UX is just look and feel/visual design.
I'd recommend reading Erika Hall's "Just Enough Research" (don't worry, it's a slim volume).
You may not have enough data to go to mockups (which, it seems, will be one step away from coding a product). I don't know how you got your feedback from these potential customers, but I'd caution that putting something in front of people and asking, "do you like this?" or "would you buy this?" is a known vector for bad data. It's like asking people what they watch on TV. They want to make you feel good and they unconsciously give you the answer they think you want. Again, Erika's book.
That is true, that an older, less techy audience may not need or want an app. That's a great insight, and one I've found in research. So maybe you shouldn't be building an app? How about a service? How about something people can call a live person and get answers? Build for the users' needs (and learn what the users' needs are), not for your own, or what's easiest. The last is a recipe for being irrelevant.
Look and feel is last. User experience (research and empathy) comes before wireframing and waaaay before coding.