Fulham were beaten 2-1 in their opener at Ipswich last Saturday.
In his letter, Magath said: "The performance was very encouraging. Ten of our starting 11 were new to the team and we finished the match with an average age of 21."
He added that it was necessary to make wholesale changes after relegation, promoting youngsters from the club's academy and releasing several senior players.
"The reason for the release of so many was that I felt that the squad was an ageing one that urgently needed to be freshened up with younger, hungrier and more ambitious players.
"I do feel that we as a club should not be frightened of change and that we need to look forward with a much younger team.
"I would like to stress that our aim is to develop a squad that can not only perform well and achieve our goal in the Championship, but grow into a strong Premier League team with a promising future."
Fulham face London rivals Millwall in their first home game on Saturday.
(Writing by Steve Tongue, editing by Tim Collings)
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