Most folks that I have started shooting traditional archery, that had problems reaching "full draw", were back to the corner of thier mouth in about a week. Usualy we spend about 1/2 to 1 hour a day, SLOWLY shooting 1 arrow at a time... It may be 10-20 arrows at first, maybe 30 or so by the end of the week. When they show the 1st signs of getting tired, we STOP!!! When they can reach the corner of thier mouth, they take the bow & a few arrows home with them... I've NEVER had anyone develope "bad habits" or have any injuries, while I've been teaching them...
Case in point... My youngest son Kevin, started shooting at 8 yrs old. I had given up archery totaly years before and had just bought a 55# Kodiak Mag, from Joe Skipp here. After a few days of shooting, Kevin wanted to try it. I got him about 5yrds from the backstop & let him shoot a few arrows. He only managed to draw the heavy bow about half way to his face, but he was seriously trying!!! After a couple days, he had his thumb knuckle to the corner of his mouth. He shot this way a few times over the next couple weeks...
About 2 weeks after I started Kevin shooting, I went over to Joe's shop to buy a backquiver. Joe had a 40# Bear Grizzly on the rack that caught my eye... Joe said,"If you want it,you better buy it, because Wayne's had his eye on it for his girlfriend" Well, the backquiver would have to wait...
That weekend, I took Kevin out in the back yard. He could easily draw the bow back to his thumb knuckle at the corner of his mouth. We shot for about an hour that morning & about an hour later that evening. The next morning after breakfast, we went out to shoot & I had him draw back the extra inch to his 2nd thumb knuckle.(below his thumb nail) He easily gained the extra inch & weight... We shot morning & evening that day and he was starting to show consistancy... Monday after school, we went out back to shoot. I had him draw to his index finger at the corner of his mouth. He did this fairly easily & we slowly shot 1 arrow at a time, untill he started showing signs of getting tired... He didn't want to stop,but I told him "tomorrow's another day!" We shot every day after school that week & by the next weekend, He was consistantly at full draw. He was "officialy" drawing 25" In his teenage years, He was one of the best 3-D shooters in our area, giving grown men a run for thier money!!! I have BOXES of trophys put away that the boys have won over the years.
As I said before, with work, It doesn't take long!!! I really see no need to spend money on extra limbs, for a (perfectly good) $150 bow...