I suggest you evolve it at lv.39. It learns Double Edge at that level and this is useful since Skitty>>>>>Delcatty have better offensive power then Sp. Offensive Power. After level 39 Skitty and Delcatty don't learn any other moves in generation III.
I still do recommend that you teach Skitty specially attacking moves since it doesn't have much acces to offensive moves.
Hope this helped