Year	Age
1970	1.7
1971	1.8
1972	1.8
1973	1.9
1974	2
1975	2.1
1976	2.3
1977	2.4
1978	2.5
1979	2.6
1980	2.7
1981	2.9
1982	3
1983	3.1
1984	3.3
1985	3.4
1986	3.5
1987	3.7
1988	3.8
1989	4
1990	4.1
1991	4.3
1992	4.4
1993	4.6
1994	4.7
1995	4.9
1996	5
1997	5.2
1998	5.3
1999	5.5
2000	5.6
2001	5.8
2002	5.9
2003	6.1
2004	6.2
2005	6.4
2006	6.5
2007	6.7
2008	6.8
2009	6.9