yellowing leaves??

my plant is nearly 5wks old, it is growing well but the lower parts leaves are yellowing a bit whats this from. theyare a bit shaded from the light wud this b the cause or n deficiiency???

any pics.
yellowing on fan leafs and lower partss is ok when flowering.
but 5 weeks old, i dont know
what are you feeding and how often.
pics would really help.