Year	Age
1970	2.7
1971	2.8
1972	3
1973	3.1
1974	3.2
1975	3.3
1976	3.5
1977	3.6
1978	3.7
1979	3.9
1980	4
1981	4.1
1982	4.3
1983	4.4
1984	4.5
1985	4.6
1986	4.8
1987	4.9
1988	5
1989	5.2
1990	5.3
1991	5.4
1992	5.6
1993	5.7
1994	5.8
1995	6
1996	6.1
1997	6.3
1998	6.4
1999	6.6
2000	6.7
2001	6.8
2002	7
2003	7.1
2004	7.3
2005	7.4
2006	7.5
2007	7.7
2008	7.8
2009	8