Year Age 1970 4.8 1971 5 1972 5.2 1973 5.3 1974 5.5 1975 5.7 1976 5.9 1977 6.1 1978 6.2 1979 6.4 1980 6.6 1981 6.8 1982 7 1983 7.2 1984 7.4 1985 7.6 1986 7.7 1987 7.9 1988 8.1 1989 8.3 1990 8.5 1991 8.6 1992 8.8 1993 9 1994 9.2 1995 9.3 1996 9.5 1997 9.6 1998 9.8 1999 10 2000 10.1 2001 10.2 2002 10.4 2003 10.5 2004 10.7 2005 10.8 2006 10.9 2007 11.1 2008 11.2 2009 11.3