I define self development as preparing oneself to be effective and efficient in attaining set goals and visions.
Of what use is it when you develop yourself in farming and you end up teaching, or developing yourself in music and you never have a chance to sing or play a musical instrument. Therefore I submit to you that it is important to have a sense of direction early in life in that area you have a gifting or you are being called into so that your efforts at preparing can be channeled wisely and more effectively in the right direction .
For the Christian, you have the Holy Spirit who can give you an insight early enough into what area you’ve been called or what your life assignment is. The same Holy Spirit can direct you and aid you at preparing adequately.
In life there are stages, there is a time to prepare and there is a season to manifest. You don’t manifest when you should be preparing and vise-versa. Therefore know what season you are presently, and maximize it now.