Level G takes about two years to complete. My son was able to finish it in a little more than 1 1/2 years, but that was really pushing through.
RightStart Math suggests that we start VideoText Algebra when the student gets to about Lesson 80 in Level G. I must say, however, that my son really wanted to just focus on geometry and finish it up prior to starting algebra. If you choose to do this, I HIGHLY recommend that you keep up your son's math facts by continuing to play the Math Card Games and/or the multivides.
Let me know if you have any further questions!
Rachel