Year	Age
1970	3.4
1971	3.5
1972	3.7
1973	3.9
1974	4.1
1975	4.3
1976	4.5
1977	4.7
1978	4.9
1979	5.1
1980	5.3
1981	5.5
1982	5.7
1983	6
1984	6.2
1985	6.4
1986	6.6
1987	6.8
1988	7
1989	7.2
1990	7.4
1991	7.6
1992	7.8
1993	8
1994	8.2
1995	8.4
1996	8.6
1997	8.8
1998	9
1999	9.2
2000	9.3
2001	9.5
2002	9.7
2003	9.9
2004	10
2005	10.2
2006	10.3
2007	10.5
2008	10.6
2009	10.8