I let my daughter eat baby food in addition to regular food right up to 1 year. I just gradually decreased what jar foods she was getting, and increased the amount of milled foods (I just ground up what we were eating, like beef stew with a lot of the liquid strained out already, or chicken and dumplings). The last thing we eliminated was jar fruits, but we continued with the baby oatmeal cereal until she didn't really want that anymore and was happy to eat regular oatmeal or cereal with us. It took her a really long time for her teeth to start coming in so we did softer foods much longer.
The only danger in feeding babies jar food too long is that they become accustomed to preferring the smooth texture of the jar food. Their swallowing needs to advance to accepting other kinds of textures. It's a good idea to offer little bits of anything they seem interested in, as long as it's an appropriate food for their age and palate, and to not be discouraged if they don't like something right away. I saw a documentary on the BBC once that was about picky eaters and it takes about 11 times of being casually and repeatedly offered a new food for a child to potentially accept it.
(And to tell you the truth, my mother allowed me to eat 1 kind of jar baby food until I was about five years old: Gerber strained plums. I loved them. It was a special treat.)