Common practice is to give solid food to a kitten at 4 weeks
age, but is there any known problems if solid feeding starts
earlier? I have heard rumours that early solid feeding might
cause allergy, but is there any studies about it?

--
"Eons came and went. At last, the first sound broke the silence.
Rhythmic and insistent, charged and vital. Every corner was filled
with awe and comfort, comfort and awe. But there were no cats yet to
know the glory that was the first purr." -- G. King: "The Wild Road"