From data.gov.au gives all sorts. of information This page here gives all sorts of data. The second one from the top gives the number of vehicles by year, type, and numbe, issued in 2023.
I can't be bothered all the states by year, so below is the passenger vehicles by year for NSW. If you look at the last 10 years from 2022. The average number of vehicles sold per year is 254k. If you go back 25 years from there that's 1997and the number remaining on the road was 21.5k. So less than 10% and dropping rapidly!
I think it's interesting. It backs up why your niece and I have been saying. :D.  Most cars make it through the first ten years, but after that it really starts dropping off quickly. 
The way averages work a few oldies can really skew the figures. Can I be bothered calculating the median? Hmmmm...
| 2012 | 230564 | 
| 2013 | 247774 | 
| 2014 | 245228 | 
| 2015 | 278392 | 
| 2016 | 287595 | 
| 2017 | 286823 | 
| 2018 | 263860 | 
| 2019 | 245450 | 
| 2020 | 216946 | 
| 2021 | 263928 | 
| 2022 | 213501 | 
|  |  | 
| 1912 | 3 | 
|  |  | 
| 1914 | 3 | 
| 1921 | 3 | 
| 1922 | 0 | 
| 1923 | 49 | 
| 1924 | 13 | 
| 1925 | 21 | 
| 1926 | 27 | 
| 1927 | 54 | 
| 1928 | 217 | 
| 1929 | 102 | 
| 1930 | 80 | 
| 1931 | 40 | 
| 1932 | 238 | 
| 1933 | 63 | 
| 1934 | 238 | 
| 1935 | 68 | 
| 1936 | 75 | 
| 1937 | 85 | 
| 1938 | 54 | 
| 1939 | 75 | 
| 1940 | 48 | 
| 1941 | 10 | 
| 1942 | 11 | 
| 1943 | 4 | 
| 1944 | 12 | 
| 1945 | 0 | 
| 1946 | 34 | 
| 1947 | 56 | 
| 1948 | 112 | 
| 1949 | 98 | 
| 1950 | 113 | 
| 1951 | 123 | 
| 1952 | 89 | 
| 1953 | 143 | 
| 1954 | 208 | 
| 1955 | 297 | 
| 1956 | 307 | 
| 1957 | 460 | 
| 1958 | 311 | 
| 1959 | 409 | 
| 1960 | 396 | 
| 1961 | 327 | 
| 1962 | 538 | 
| 1963 | 741 | 
| 1964 | 1298 | 
| 1965 | 1200 | 
| 1966 | 1383 | 
| 1967 | 1402 | 
| 1968 | 1422 | 
| 1969 | 1614 | 
| 1970 | 2098 | 
| 1971 | 2237 | 
| 1972 | 1515 | 
| 1973 | 1509 | 
| 1974 | 1734 | 
| 1975 | 1357 | 
| 1976 | 1486 | 
| 1977 | 1414 | 
| 1978 | 1297 | 
| 1979 | 1097 | 
| 1980 | 794 | 
| 1981 | 927 | 
| 1982 | 1149 | 
| 1983 | 1125 | 
| 1984 | 1806 | 
| 1985 | 2517 | 
| 1986 | 1886 | 
| 1987 | 1676 | 
| 1988 | 2576 | 
| 1989 | 3990 | 
| 1990 | 5361 | 
| 1991 | 5600 | 
| 1992 | 6669 | 
| 1993 | 8130 | 
| 1994 | 10575 | 
| 1995 | 12296 | 
| 1996 | 14764 | 
| 1997 | 21559 | 
| 1998 | 30930 | 
| 1999 | 37882 | 
| 2000 | 50596 | 
| 2001 | 56620 | 
| 2002 | 72507 | 
| 2003 | 97584 | 
| 2004 | 111655 | 
| 2005 | 128580 | 
| 2006 | 138855 | 
| 2007 | 164045 | 
| 2008 | 167809 | 
| 2009 | 166579 | 
| 2010 | 199176 | 
| 2011 | 200493 | 
| 2012 | 230564 | 
| 2013 | 247774 | 
| 2014 | 245228 | 
| 2015 | 278392 | 
| 2016 | 287595 | 
| 2017 | 286823 | 
| 2018 | 263860 | 
| 2019 | 245450 | 
| 2020 | 216946 | 
| 2021 | 263928 | 
| 2022 | 213501 |