The Guardian has an 'ask the astrologer' type column in which I found this exchange:

Q Is it possible to have a 'Saturn Return' outside of the 28- to 30-year cycle? Are there any positive connotations to Saturn? I am accustomed to thinking of it as an influence to fear.

A You aren't alone in fearing Saturn, but no planet is all bad, and when you're under saturnine skies you can and should undertake something big which demands patience, exactitude and strength of will. Saturn 'returns' (ie completes an orbit round the Sun) at ages 28-30, 58-60, 88-90, but the quarter and half points of the cycle - ages 7, 14-15, 21, etc - often show up as challenging and transitional times in people's lives.

I wonder if there's a connection between this and the concept of an annus climacterius, which the Romans believed happened at these very same ages (i.e. the 'quarter and half points of the cycle') ....