Just eat a low calorie diet. If you aren't obese you will live longer than average. Specialized diets just make your life miserable.
I'd say just find a way of eating that works for you, meaning it provides you with health benefits, helps keep you lean long term, and it's enjoyable and sustainable long term. It doesn't matter whether it's omnivore, vegetarian, vegan, or carnivore.
A low carb, high fat diet is a low calorie diet too for most people because hunger and cravings go away and they end up eating less calories without trying. That's one of the reasons these diets work for weight loss.
A calorie restricted diet for longevity is a specialized diet too and it's extreme, and if done high carb it will make your life miserable. I'd rather live a shorter happier life than a longer miserable one.
Over many years I tried pretty much every diet there is, even vegan for 3 months. I was always miserable because of chronic health issues I had developed over time. I often just ate things I don't enjoy because "they're good for me." I also ate things I did enjoy, but made me feel guilty because "they're not good for me." I've been in very good shape and in poor shape on and off my whole life, but miserable most of the time and my quality of life was poor.
I finally found that a very meat heavy, keto diet is the way of eating that I personally enjoy most, provides me with many health benefits, provides me constant satiety, helps keep me lean consistently long term, gives me a lot of energy and mental clarity, it's delicious and keeps me happy. Not to mention I don't miss all the gas and bloating that plant-based foods give me.
I'm going on almost four years now, and so far I plan to do this for the rest of my life. My quality of life is better than ever, and I no longer eat anything I don't enjoy.