To what do Mrs. Who and Mrs. Which attribute the fact that Mrs. Whatsit has an easier time of speaking in words that they do

Mrs. Whatsit has an easier time speaking in words because she is young.

Mrs. Which shook her head. "Nnott heeere, Megg. Llett Mrs, Whatsitt expllainn. Shee isss yyoungg annd thee llanguage of worrds iss eeasierr fforr hherr thann itt iss fforr Mrs. Whoo andd mee."