Year	Age
1970	2.1
1971	2.2
1972	2.3
1973	2.4
1974	2.4
1975	2.5
1976	2.6
1977	2.7
1978	2.8
1979	2.9
1980	3
1981	3.1
1982	3.2
1983	3.4
1984	3.5
1985	3.6
1986	3.6
1987	3.6
1988	3.6
1989	3.7
1990	3.7
1991	3.7
1992	3.8
1993	3.9
1994	3.9
1995	4
1996	4.1
1997	4.2
1998	4.2
1999	4.3
2000	4.4
2001	4.5
2002	4.6
2003	4.7
2004	4.8
2005	4.9
2006	5
2007	5.1
2008	5.2
2009	5.3