Year	Age
1970	1.7
1971	1.8
1972	1.9
1973	2
1974	2.2
1975	2.3
1976	2.4
1977	2.5
1978	2.7
1979	2.8
1980	3
1981	3.1
1982	3.3
1983	3.5
1984	3.6
1985	3.8
1986	4
1987	4.2
1988	4.4
1989	4.5
1990	4.7
1991	4.9
1992	5.1
1993	5.3
1994	5.5
1995	5.7
1996	5.8
1997	6
1998	6.2
1999	6.4
2000	6.6
2001	6.8
2002	7
2003	7.1
2004	7.3
2005	7.5
2006	7.7
2007	7.9
2008	8
2009	8.2