To be honest my first child was speaking in a complete sentence when he was 12 months old, people don't believe me either, but he did. He knew all of his letters by 14 months as well.
You haven't worked with him at all?
I have worked with mine since 6 months old, to get the results we do now.
Does anyone in your family have a photographic memory? or have a high IQ?
I am not an expert but if you haven't worked with him on a daily bases or not all then I would say you do have a smart gifted child who enjoys to learn.
I say go for it, teach him/her all that they can take, but have fun, fun, fun, and read, read, read.
And being a homeschool mom/teacher you may want to think about later on homeschooling, that is if your public school system does not have the capability to advance your child when needed. Some of the public schools here do not have the resources to advance a child when needed based on their level, they just let them hang out instead of nuturing their gift allowing the child to reach his/her full potention, something to think about in the future.
Oh and whatever brain food you are feeding him/her kepp it up!
my suggestion is to start recording or documenting your child's abilities every day, set a routine up if can for educationa, read a book, etc. Also you may want to think about when he/she recognizes a word, and can actually read the word then record it. you maight be amazed at all he/she knows by the end of the month.
Also for a great phonics website when you get to that point, for I also have a 16 month old and we have been doing this for several months now, it is
www.dreamenglish.com sorry that is if you speak English, or plan on teaching english.