A 7 year old needs to begin 9 months ahead. forward slowly, one page per week, plus polish on the way. At the same time, find the technical weakness, practice supplimentary songs to fix technics. After first round of full song, use 8 weeks to play full song, inspire the students' emotion feeling of the concerto, probablly need play other supplimentary songs to bring out the understanding. then take 8 week break to play other songs the kid likes. Let the student relax fully.
Then use 2-3 weeks to bring back the whole conerto. by now the student should able to discover and aufo-fix any the technical weakness, and show emtions.
then practice with an accompanist. Need at least 2-3 months to learn how to cooperate with an accompanist if this is the first concerto of the student.
Last month, stop all other songs, only intensively pracitice this concerto, perform weekly in different size of halls of public or semi public.
when the kid is 8 year old, his second conerto will only needs half the time to prepare.