Year	Age
1970	2.7
1971	2.8
1972	3
1973	3.1
1974	3.3
1975	3.4
1976	3.6
1977	3.7
1978	3.9
1979	4.1
1980	4.3
1981	4.4
1982	4.6
1983	4.8
1984	4.9
1985	5.1
1986	5.3
1987	5.4
1988	5.6
1989	5.8
1990	5.9
1991	6.1
1992	6.2
1993	6.4
1994	6.6
1995	6.7
1996	6.9
1997	7
1998	7.2
1999	7.4
2000	7.5
2001	7.7
2002	7.8
2003	8
2004	8.1
2005	8.3
2006	8.4
2007	8.5
2008	8.7
2009	8.8