Year	Age
1970	4
1971	4.1
1972	4.3
1973	4.4
1974	4.6
1975	4.8
1976	4.9
1977	5.1
1978	5.2
1979	5.4
1980	5.5
1981	5.7
1982	5.9
1983	6
1984	6.2
1985	6.3
1986	6.5
1987	6.6
1988	6.7
1989	6.9
1990	7
1991	7.2
1992	7.3
1993	7.4
1994	7.6
1995	7.7
1996	7.8
1997	8
1998	8.1
1999	8.3
2000	8.4
2001	8.5
2002	8.6
2003	8.8
2004	8.9
2005	9
2006	9.1
2007	9.3
2008	9.4
2009	9.5