He is a '00 snake, so about 3.5 years. And I wouldnt feed a snake 3-4 times a week. Powerfeeding isnt good at all for a snake. Shortens the lifespan and could cause it to have health problems. You will have a healthier snake if you feed it twice a week as a hatchling - yearling or a year and a half old, and once a week after that. Your snake may or may not achieve the 4'+ length. Not all corns will get that big, but then some can attain 5.5' or maybe close to 6'. Never seen one that big, but Im sure that some are that close.
Just take your time with it and enjoy the changes it goes through and it will be a more healthy snake in the long run.
If you want a snake that can get pretty long and have about the same disposition as the corn, get yourself a black rat snake. They come in all kinds of morphs, although not as many as the corn. The black rat can attain the 6' mark easily and I think the record is 101"!! I Have an albino that has just kick @ss colors and they are available in brindle, rootbeer, and whitesided as well! Then you have the black rats in KY that never lose their pattern and retain much of their coloration.
My albino '02 Dwight Good stock

And my KY locale black rat, '01

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Good luck and Happy Herping
Brian