Strength training definitely has its effect on overall health. It's not just the training itself, but other things related to it may add to your health and longevity. Let's focus on a few ground rules. Body, when taken care of properly, stays health and fit. When you do strength training, you not only get stronger and gain muscles, but in order to do that, you eat clean, you sleep well, drink a lot of water and stay away from unhealthy practices like smoking, recreational drugs and heavy drinking. Why, because body building is a discipline and those who do it, they keep it in mind. All these activities keep the body functioning normally. That's what you call the maintenance of the body. So anything maintained throughout, would last longer.
Having said that, doing it for a year may yield you some short teams benefits, but to live longer, you have to keep doing it along with other things that I have mentioned above. As always, there's no guarantee that anyone would live longer due to strength training or all other practices followed due to it, but it definitely increases your chances to it. Also, you have to do it correctly, to avoid injuries.