Year	Age
1970	3.7
1971	3.9
1972	4.1
1973	4.3
1974	4.5
1975	4.6
1976	4.8
1977	5
1978	5.2
1979	5.4
1980	5.5
1981	5.7
1982	5.9
1983	6
1984	6.2
1985	6.4
1986	6.5
1987	6.7
1988	6.8
1989	7
1990	7.1
1991	7.3
1992	7.5
1993	7.6
1994	7.8
1995	7.9
1996	8.1
1997	8.3
1998	8.4
1999	8.6
2000	8.7
2001	8.9
2002	9
2003	9.2
2004	9.3
2005	9.5
2006	9.6
2007	9.7
2008	9.9
2009	10