Year	Age
1970	2.2
1971	2.3
1972	2.4
1973	2.5
1974	2.7
1975	2.8
1976	3
1977	3.1
1978	3.2
1979	3.4
1980	3.6
1981	3.7
1982	3.9
1983	4
1984	4.2
1985	4.4
1986	4.5
1987	4.7
1988	4.9
1989	5
1990	5.2
1991	5.4
1992	5.5
1993	5.7
1994	5.9
1995	6
1996	6.2
1997	6.4
1998	6.5
1999	6.7
2000	6.9
2001	7
2002	7.2
2003	7.4
2004	7.5
2005	7.7
2006	7.8
2007	8
2008	8.1
2009	8.3