But, the most important thing is to never give up. I can't argue that there is no upper limit to skill (those weirdos trying to 1cc Dodonpachi for example :V), but you shouldn't sell yourself short if you truly want to succeed.
:V Prometheus, that guy with the 2-all I mentioned to you, is an advocate of the idea that there isn't an upper limit for skill; IIRC, he's been playing DDP for a little over 6 years and made constant small improvements over that time period.
Stop telling me I can't do it. ;_;As for myself, I would rate my random dodging skills (i.e. what a lot of people consider actual skill at danmaku) as maybe average? A little above average at best. Despite that, over the course of 14 months or so I worked myself up through the series until managing to 1cc UFO Lunatic, often cited as incredibly difficult even amongst the other Lunatic modes. Practicing the games by themselves will help a little bit but it's not really what you're looking for; the key for effective practice is focusing on specific areas of the game. Go through the game until you encounter some kind of problem, whether it's dying with bombs in stock, or a particular stage segment, or a specific spell card, or a certain type of bullet pattern (I know a lot of people have trouble with interlaced-style bullet patterns like you see in Hourai Elixir and Mishaguji-sama), and then practice that until you either get good at it or write it off as a designated bombing spot.
Like this, even a player new to the genre can 1cc a game - on a related note, it's been proven that MoF, on any difficulty, can be beaten by bombing every single attack a boss throws at you and still have a significant amount of bombs left over; this kind of contradicts the idea that some players are unable to beat certain difficulty levels, and I think a player who considers themself to be a Normal mode player could 1cc MoF on Lunatic,
given the proper preparation. Bananamatic and others have already pretty much mentioned most of what I wanted to say, but I'll just reiterate that no-one is obligated to be able to beat the game on any difficulty level, but you have the capability to do damn near anything if you're enjoying yourself enough to warrant the playtime, experimenting and research required.
Sorry if this was kind of incoherent; just got back from an Opeth concert and I'm a little out of it. :V