At what age does working memory peak?

Working memory performance peaks in the twenties and declines slowly afterwards. Simple digit span holds up well into the 60s, dropping by only about one item on average between ages 20 and 70. Tasks that require juggling or reordering information decline earlier and faster, and processing speed begins its slide in the 30s.

Source: Park et al. (2002), Psychology and Aging; Bopp & Verhaeghen (2005), Journals of Gerontology B