Year Age 1970 3.3 1971 3.4 1972 3.6 1973 3.8 1974 4 1975 4.2 1976 4.4 1977 4.6 1978 4.8 1979 5 1980 5.2 1981 5.4 1982 5.7 1983 5.9 1984 6.1 1985 6.3 1986 6.5 1987 6.8 1988 7 1989 7.2 1990 7.4 1991 7.6 1992 7.8 1993 8.1 1994 8.3 1995 8.5 1996 8.7 1997 8.9 1998 9.1 1999 9.3 2000 9.5 2001 9.7 2002 9.9 2003 10.1 2004 10.3 2005 10.5 2006 10.6 2007 10.8 2008 11 2009 11.2