Year	Age
1970	2.1
1971	2.2
1972	2.3
1973	2.4
1974	2.5
1975	2.7
1976	2.8
1977	2.9
1978	3.1
1979	3.2
1980	3.4
1981	3.5
1982	3.7
1983	3.8
1984	4
1985	4.1
1986	4.3
1987	4.5
1988	4.6
1989	4.8
1990	4.9
1991	5.1
1992	5.3
1993	5.4
1994	5.6
1995	5.8
1996	5.9
1997	6.1
1998	6.3
1999	6.5
2000	6.6
2001	6.8
2002	7
2003	7.1
2004	7.3
2005	7.5
2006	7.6
2007	7.8
2008	8
2009	8.1