Year	Age
1970	1.8
1971	1.9
1972	2
1973	2.2
1974	2.3
1975	2.4
1976	2.6
1977	2.7
1978	2.9
1979	3
1980	3.2
1981	3.4
1982	3.6
1983	3.8
1984	3.9
1985	4.1
1986	4.3
1987	4.5
1988	4.6
1989	4.8
1990	5
1991	5.2
1992	5.4
1993	5.6
1994	5.7
1995	5.9
1996	6.1
1997	6.3
1998	6.5
1999	6.7
2000	6.9
2001	7.1
2002	7.3
2003	7.4
2004	7.6
2005	7.8
2006	8
2007	8.1
2008	8.3
2009	8.5