Year	Age
1970	4.7
1971	4.9
1972	5
1973	5.2
1974	5.4
1975	5.5
1976	5.7
1977	5.8
1978	6
1979	6.1
1980	6.3
1981	6.5
1982	6.6
1983	6.8
1984	6.9
1985	7.1
1986	7.2
1987	7.4
1988	7.5
1989	7.7
1990	7.8
1991	8
1992	8.1
1993	8.3
1994	8.4
1995	8.6
1996	8.7
1997	8.9
1998	9
1999	9.2
2000	9.3
2001	9.5
2002	9.6
2003	9.8
2004	9.9
2005	10
2006	10.2
2007	10.3
2008	10.4
2009	10.6