I think that is optimistic for a seedling. I'd guess my native trees are about 10 years or so old when they first produce. You can probably cut a few years off by grafting. Trees typically focus their energy on vegetative growth until they hit a certain level of maturity when the focus changes to reproduction. I think it controlled with hormones. Presuming you take the scion from a mature, fruit producing tree, it has a different hormone make-up than the rootstock. I think this may cut you down to about 8 years.
Keep in mind that I'm suggesting this is an average for my native trees. What I see advertised from nurseries is very optimistic for most trees. Some trees will produce at a younger age and some will take longer. Good care and planting location probably shorten things a bit.
If I cut down a native tree that is an inch or more in diameter and bark graft it, it is not uncommon to get the first few fruits in the third leaf.
Thanks,
Jack