Year	Age
1970	2.8
1971	2.9
1972	3.1
1973	3.2
1974	3.3
1975	3.5
1976	3.6
1977	3.8
1978	3.9
1979	4.1
1980	4.2
1981	4.4
1982	4.6
1983	4.7
1984	4.9
1985	5.1
1986	5.2
1987	5.4
1988	5.5
1989	5.7
1990	5.9
1991	6
1992	6.2
1993	6.4
1994	6.5
1995	6.7
1996	6.9
1997	7
1998	7.2
1999	7.4
2000	7.5
2001	7.7
2002	7.9
2003	8
2004	8.2
2005	8.3
2006	8.5
2007	8.6
2008	8.8
2009	9