Year	Age
1970	4.2
1971	4.3
1972	4.5
1973	4.7
1974	4.8
1975	5
1976	5.1
1977	5.3
1978	5.5
1979	5.6
1980	5.8
1981	5.9
1982	6.1
1983	6.3
1984	6.4
1985	6.6
1986	6.7
1987	6.9
1988	7
1989	7.2
1990	7.3
1991	7.5
1992	7.6
1993	7.7
1994	7.9
1995	8
1996	8.2
1997	8.3
1998	8.4
1999	8.6
2000	8.7
2001	8.8
2002	9
2003	9.1
2004	9.2
2005	9.4
2006	9.5
2007	9.6
2008	9.7
2009	9.8