I frequently hear people speak of some guitarists as being ‘naturals’. Where guitar playing is a skill, the guitar itself (in it's current form) is an instrument which has had its basic shape and form invented, and then it has gone through a process of evolution. A guitar is not a natural instrument like the voice. As such, how can you attribute anything regarding the skills people need to play a guitar to be in any way natural?
The nature of a skill is that it is learned. Where there are people who have an aptitude for learning certain things at different speeds from others, that isn’t the acquisition of the skill itself, that’s the speed at which the skill is acquired. The skills required to play the guitar are obtainable by anyone (of ‘normal’ physical and mental capability) because of the nature of what a skill is.
If anyone has concerns about whether or not it’s possible to obtain the skill of guitar playing, they are unfounded. If anyone has concerns about how fast these skills may be developed, this is simply a question of how much effort you need to make. After that it’s just a matter of discipline, determination and perseverance. How much of each of these three things that you will need is relative to how good you want to be.