For an average amount of time? Assuming he's playing a few hours a week, maybe 6 or 7 from a few matches a day, it'd probably take him about 8 to 10 months. It took me a year and a half, and that was mainly because I stopped playing for a good four or five months when I got a bit too busy with two jobs to really worry about spending upwards of 45 minutes of my day playing a game I could possibly lose at.
Try and remember how tough the climb to 30 was for you. Remember how frustrating it could be not understanding why things were happening in the game. Little things that we've come to understand now, that are second nature to us now, are entirely foreign concepts to a new player and take a lot of time to not simply get used to, but to learn innately the way we have as level 30 players. Chances are he's going to become discouraged, like many people have. I stopped playing from a combination of lack of time and overall not feeling like I was getting any better. When I came back, grinded my way up to the mid twenties, I started to really feel like I understood what was happening and why.
At this point I really do feel sorry for players who are new to the game. There's, what, 150 or so champions? Each with 5, or more, abilities that you need to learn what they do and how to avoid them. Each with several build paths comprised of a multitude of items that provide an innumberable amount of effects. DOTA players may like to brag about how it's a harder game than League, and in many instances I'm going to agree. Mechanically speaking it's MUCH more difficult. But on a knowledge basis you still have to start near the ground level no matter whether you're a MOBA scrub like I was or a seasoned DOTA player. There's still a learning curve, and every player has to tackle that upwards climb.
And for the love of all things tiny and evil, do NOT let your friend spend RP on champions until he hits level 30 and won't be wasting potential refunds, and do NOT let him buy tier 1/2 runes.
I wish I could say that I'd love to help him learn the game, I'm a jungle main so I can camp out a lane like nobody's business, but that would be just a bit of a stretch. I do have a job and other real world duties to attend to and I can't exactly be on holding people's hands, you know? All the same I wish him the best, and if you guys ever need a jungler to show your lanes some love hopefully we play matches together sometime.
