I may be off, but i'm pretty sure that most will come pretty true from seed. What kind of grapefruit was it? Thats pretty interesting if they are already flowering after 1 year. I've got citrus (not even sure what they are) that are 4 years old and 6 feet tall and still no flowers! (it can take 10 years).

Wow, flowers and fruit on a year old seedling! I didn't think that was possible. Post some pictures; perhaps someone can give you an idea about what they might be from that.

Will try and get some pictures. I do not think there are any flowers left but last time I looked there were fruit about the size a BB.
Beerhog

Here are some pictures. The fruit had fallen off the plant but found it on the ground. There were not anymore flowers on it.

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Beerhog

They are not grafted. I grew them for seed taken out of a grapefruit.

I have grown a grapefruit tree from a seed which was sprouting inside the fruit. It has been about twenty three years and it has produced its first friut (14 full size)which I picked today. I have the tree put in a greenhouse during the winter months and bring it back out in April. April this year it flowered and the rest is history.

Just to chime in, you must be doing something that the tree loves. To have that type of fruit on the first year. WOW. Did you have to do something special. Do you have more than one. Do they need to polinate?? Mine seems healthy but has never flowered and shows no signs of even thinking about it.
Kari

It is not uncommon for grapefruit seedlings to flower in their first or second year. The same applies to pummelos and a few hybrids of these species. The flower is always a single terminal bud. Usually it falls off when still tiny, but I once managed to produce a small ripe fruit by supporting it in a net while it was growing.
These early flowering plants will not flower again until the normal juvenile period is over. Some people in ideal climates say it takes 6-8yrs for a grapefruit. Here in the UK I have found 12 to 15 years is normal, but chris61's 23 years doesn't surprise me. Congratulations on keeping faith for so long - many people give up after a couple of years!