I have read in various forums about kumquat not doing well on its own roots. Can someone clarify what problems they run into?? Is it reduced growth or susceptibilty to root rot..

Also, how many years will it take to bloom and bear fruit?

From memory, Fortunella are said to be prone to a nutrient deficiency ( I think it was Zinc) that causes major root problems. Eventually seedlings decline and die.I will try to update this post with correct info. re Zinc?? On the other hand, I have found F. hindsii seedlings very tough, F. margarita Nagami ok, but F.crassifolia weaker on its own roots. Maybe it depends on what Fortunella your seedling is ?

I have a different question. How long does it usually take for Kumquats to flower/fruit from seed?

I grew some seeds from Meiwa. Are they just going to be clones from the mother plant? Or am I going to get something unique? I think the seedlings came out to be monoembryonic, but I'm not sure if that was the case (perhaps it was poly and I didn't see it)...

I do notice that the seedlings have baby spines and the petioles are a little leaf-like.

I have 2 Meiwa from seed in pots, one flowered and fruited after about 10 years. The fruit seem identical to Meiwa, the plant is more vigorous and thorny(so far). Your seedling, as is mine, will show juvenile characters for a while, compared to any bud lines used in grafting etc. Also it may not have any viruses carried by the scion (bud line), so it may grow better if budded onto rootstock.
I grew a lot of Meiwa seedlings looking for a variegated, and never saw any differences in the seedlings at all, but there are the above "differences" from the seed parent.
Even in clonal polyembryonic seedlings you would expect some tiny differences in the seedlings due to mutation or recombination, but if you cant see any difference such as longer leaves or shorter thorns etc you cant screen the seedlings for anything interesting.
I recently budded my Meiwa onto rootstock to see if it grows faster than the original grafted scion, but there is still a question about how well it fruits, apart from simply producing fruit.