There is, unfortunately, a genetic component to musical ability. That doesn't mean that practicing won't help - in fact, it helps everyone regardless of age or ability - but there are certain genetically inherited traits.
From a 2014 article in Scientific American,
http://www.scientificamerican.com/article/what-do-great-musicians-have-in-common-dna/
"A similar study forthcoming in Psychological Science by Miriam A. Mosing of Stockholm's Karolinska Institute leans even heavier on the role of genes in musicality. Mosing and colleagues looked at the association between music practice and specific musical abilities like rhythm, melody and pitch discrimination in over 10,000 identical Swedish twins. They reported that the propensity to practice was between 40% and 70% heritable and that there was no difference in musical ability between twins with varying amounts of cumulative practice. "Music practice,” they conclude, “may not causally influence musical ability and … genetic variation among individuals affects both ability and inclination to practice."
In other words, the desire to practice in the first place is partly genetic, and second, the folks with identical genes (identical twins) who have great musical ability can practice different amounts and still have the same musical ability.
Further studies show that unless the musical ability is developed through that combination of genetics and structured study before a kid is in his into adolescence, an adult learner will only get so far. It's like learning a language. Small children pick up languages faster than older folks. Apparently this has something to do with the development of neural pathways and networks in the brain.
So if you're 12 years old and you're very talented, and you're woodshedding and sitting in your room playing guitar every spare moment, you're just going to be a lot better than a person who picks up the instrument later in life, or starts that woodshedding later in life, and not only that, you're going to be able to play with other musicians better, because your innate sense of timing is better, etc.
So yes, by all means, practice, but don't expect to be Eric Johnson if you've reached adulthood, unless you were, in fact, Eric Johnson as a young kid.
I started piano lessons at four, and had some degree of musical talent. Piano has always been effortless for me, and speed isn't an issue.
I took guitar up at 17, and after many years of playing both guitar and piano professionally - I'm in my 60s now - I still feel far more comfortable on piano, I'm faster, and I'm just a far better piano player than guitar player. But...here's the good news.
Some of the greatest guitar solos of all time are not played at 800 notes per minute. I do pretty well at session work playing melodically or playing interesting combinations of notes, at relatively slow speeds, because ultimately, an interesting solo is not based on speed, it's based on note selection, timing, phrasing, etc. A great solo can be played on quarter notes instead of 1/32 notes.
So by all means practice, and at some point you'll hit the speed wall because of who you are, and not just because you need to practice more. But we all still have to play interesting phrases. And that's really the more important issue. Can you improvise an interesting solo? Do you know how to create a good melody? How's your sense of timing when playing with good musicians?