Year	Age
1970	2.5
1971	2.7
1972	2.8
1973	2.9
1974	3.1
1975	3.2
1976	3.4
1977	3.5
1978	3.7
1979	3.9
1980	4
1981	4.2
1982	4.3
1983	4.5
1984	4.7
1985	4.8
1986	5
1987	5.1
1988	5.3
1989	5.5
1990	5.6
1991	5.8
1992	5.9
1993	6.1
1994	6.3
1995	6.4
1996	6.6
1997	6.7
1998	6.9
1999	7.1
2000	7.2
2001	7.4
2002	7.5
2003	7.7
2004	7.8
2005	8
2006	8.1
2007	8.2
2008	8.4
2009	8.5