From last year 2019
4 seed grown 2 year old Meiwa kumquat trees
The last of the harvest. The center kumquat is the first fruit from the second tree to produce. It to was very good tasting.
Your pictures of the plants are quite illustrative and shows what you can achieve in a short duration (relatively speaking) with the right conditions. Citrus seems to have a pronounced "hook" when it emerges from its seed. I have noticed that quite frequently but not always.
Inspired by you I am going to try over-wintering a citrus next winter in a outdoor shed (originally a garage supposedly). I finally fixed the entrance of my shed. Used two layer Solexx panels for the front. This year I am monitoring interior temperatures and also over-wintering some temperate plants. So far it has been so mild that is annoying me in some ways.
But the idea is to create an insulated box inside the shed with one side exposed (through the Solexx panels) towards Sun. Here is a pic of the shed with a new front and a sliding door.