Year	Age
1970	2.5
1971	2.6
1972	2.8
1973	2.9
1974	3
1975	3.2
1976	3.3
1977	3.5
1978	3.6
1979	3.7
1980	3.9
1981	4
1982	4.2
1983	4.3
1984	4.5
1985	4.6
1986	4.7
1987	4.9
1988	5
1989	5.1
1990	5.3
1991	5.4
1992	5.5
1993	5.7
1994	5.8
1995	6
1996	6.1
1997	6.3
1998	6.4
1999	6.6
2000	6.7
2001	6.9
2002	7
2003	7.1
2004	7.3
2005	7.4
2006	7.6
2007	7.7
2008	7.9
2009	8