We can look at what's happening in Ukraine right now to see how well that's working. The truth of it is that no matter how much technology is deployed land can only be held with infantry.
Being infantry is still physically demanding and cannot be usefully replaced by technology. Maybe they aren't marching hundreds of kilometres on foot anymore, but they still need to endure the weather, minor injuries, and move through forests carrying heavy packs.
Physically, being infantry is beyond most people in their sixties.
That’s all true, except that something like 2/3 to 3/4 of most armies are not front line troops (support, logistics, intelligence, admin, etc.) it seems many if not most of those roles could be adequately fulfilled by people that are not particularly fit (e.g. you don’t need a 28yo doing aircraft maintenance or driving a truck)
Being infantry is still physically demanding and cannot be usefully replaced by technology. Maybe they aren't marching hundreds of kilometres on foot anymore, but they still need to endure the weather, minor injuries, and move through forests carrying heavy packs.
Physically, being infantry is beyond most people in their sixties.