Year	Age
1970	2.9
1971	3.1
1972	3.2
1973	3.4
1974	3.6
1975	3.7
1976	3.9
1977	4.1
1978	4.3
1979	4.4
1980	4.6
1981	4.8
1982	5
1983	5.2
1984	5.3
1985	5.5
1986	5.7
1987	5.8
1988	6
1989	6.2
1990	6.3
1991	6.5
1992	6.7
1993	6.8
1994	7
1995	7.2
1996	7.3
1997	7.5
1998	7.7
1999	7.8
2000	8
2001	8.2
2002	8.3
2003	8.5
2004	8.6
2005	8.8
2006	8.9
2007	9.1
2008	9.2
2009	9.3