Maddy I understand how you feel about the loss of a tradition and it is something I have been thinking of recently. Just how longstanding are many of the traditions we miss?
I think we look back to our childhoods and look at traditions we had then and assume it has always been so and get nostalgic when they go, but if we investigate, we find that they may only have started a few years before we were born.
The idea of celebrating 21 birthdays and getting the key of the door, probably didn't exist in any form before WW1. Then women did not get the door key at all and although officially of age at 21, still lived at home under their parents thumb.
I suspect the tradition didn't really get going until the 1930, when everyone, male and female got the vote at 21 and, as a result of the war, women got an independence they had never had before. Many would never marry because the men they might have married had died and they expected more from life than domestic servitude to their parents if they did not marry.
The tradition became obsolete in 1971 when the age fell to 18 and even more obsolete as young people got more and more freedom and got the key to the door at a much younger age.
This tradition really only had a life of about 50 years from the 1930s to the 1970s. Sad to see it go, yes, but there must have been 1000s of such bief traditions over the centuries. Good for a lifetime then lost and forgotten.