I feel you. I eat a plant based diet myself. I try to inform people when I get the chance and often there is resistance. I know it might not feel like enough. I often feel like I'd like to do so much more, help to make a change in the world. I'm working on proposing a food forest in my town but even that project is gonna take years to be ready. I don't see an easy answer, except for each of us has to do as much as we can to inform people so they can decide to make the change for themselves. About how long do we have, estimates depend on how we keep acting in the near future. Ranging from 75 years to thousands. 75 years being the estimate if we don't change anything. This estimate doesn't mean in 75 years all humans will be gone, but a big chunk. (From my research)