Year	Age
1970	2.8
1971	2.9
1972	3.1
1973	3.2
1974	3.3
1975	3.4
1976	3.5
1977	3.7
1978	3.8
1979	3.9
1980	4
1981	4.2
1982	4.3
1983	4.5
1984	4.6
1985	4.7
1986	4.9
1987	5
1988	5.1
1989	5.3
1990	5.4
1991	5.5
1992	5.6
1993	5.8
1994	5.9
1995	6
1996	6.1
1997	6.3
1998	6.4
1999	6.5
2000	6.6
2001	6.8
2002	6.9
2003	7
2004	7.1
2005	7.2
2006	7.3
2007	7.4
2008	7.5
2009	7.6