Would you say Aries, taurus, gemini,cancer, leo,virgo are the youngest signs in their nature and the other six the oldest, with pisces being the oldest.
So say someone who has a lot of Aries/gemini for instance in their charts would be very childlike.
And someone with a lot of capricorn/aquarius will come across as more mature. But then again saturn rules both these signs i know.
No.
This idea of maturity or enlightenment through-the-signs by the numbers was popularized by Dane Rudhyar, but his specific interest was in the horoscope as a kind of model for human personal development.
But zodiac time is circular time. Pisces is succeded by Aries. It's not linear time.
Animatrix, surely by now you are aware of the signs with modern rulers (Scorpio, Aquarius, Pisces) as having traditional rulers, as well. You might consider what rulers they could have possibly had prior to the discovery of Uranus, Neptune, and Pluto.
Many western astrologers practice traditional astrology, where the modern outer planets might have relevance as thematic rulers, but not as sign rulers due to their not fitting into the table of essential dignities.
http://www.skyscript.co.uk/essential_dignities.html
Chrysalis, it might help to consider that Aries is ruled by Mars, the planet of anger, assertiveness, and action (as the cardinal fire sign.)
Mercury rules the youthful stage of life. I do think that people with Mercury-ruled Virgo and Gemini strong in their chart tend to appear more youthful throughout life.
But a horoscope always has to be understood as a whole. Someone might have the sun in Virgo, but with a heavy Capricorn and Saturn influence, you might see more of the Saturn nature than the Mercurial nature.