Year	Age
1970	3
1971	3.1
1972	3.2
1973	3.2
1974	3.3
1975	3.4
1976	3.5
1977	3.6
1978	3.7
1979	3.7
1980	3.8
1981	3.8
1982	3.9
1983	3.9
1984	4
1985	4
1986	4.1
1987	4.1
1988	4.2
1989	4.2
1990	4.3
1991	4.4
1992	4.4
1993	4.5
1994	4.6
1995	4.7
1996	4.7
1997	4.8
1998	4.9
1999	5
2000	5.1
2001	5.1
2002	5.2
2003	5.3
2004	5.4
2005	5.5
2006	5.6
2007	5.7
2008	5.8
2009	5.9