In my opinion there is no definitive answer because most Citrus are hybrids of several original species.
Some Microcitrus can fruit from seed in 18 months,
West Indian Lime 3 years,
Mandarin 6 years,
Pummelo 10 years plus.
Citrus cultivars are complex hybrids of the above and more.
There would be different systems and genes counteracting each other at times to induce or delay flowering maturity.
What works in one case may not work for another.
On top of that there is climate, in areas of continual growth i.e. tropics, flowering and growth to node count can be achieved much faster.
Node count is a good rule, but there are certainly case of Citrus plants flowering well before it is achieved.
Presumably mutations that lessen the effect of one or more controlling genes.