It is never too late to learn proper techniques. You can indeed improve and break your bad habits. What are some examples of your bad habits? I would start back at the basics. There are plenty of apps you can download for smartphones that teach music theory, have chord charts, strobe tuners, scale charts, etc. One of my personal favorites is GuitarChords (free), which is perfect for me because I play by ear. I can't read music, I hate tabs, so all my life, I hear things and I play them, or when I write, I hear the music in my head and try my best to make it real. So GuitarChords helps me figure out the name of chords I don't know if I'm trying to play with another musician, or if I'm writing and have the idea in my head but can't find another chord for it, I try out things from the app. A great tuner app is InTuna ($0.99). It's a digital strobe tuner that gets it down to the tenth of a Hertz.
To help any rhythm troubles you may have, you can try playing along with a song or using a metronome and tapping your foot. Practice different strum patterns, mixing offbeats, upward and downward strums, etc. And learn your scales as well. Those are extremely helpful in a lot of aspects. I've never taken a lesson, but learning scales helped improve my knowledge of music theory seeing how they were put together, the notes involves, what keys they would work with. They also improved my rhythm, speed, accuracy, creativity, as well as a few other things. Eventually you can learn to throw in a quick lick into rhythm strumming.
And last of all, practice, practice, practice. Don't just set aside time every day to practice, though that's a good start. Anytime you're sitting around watching TV or something like that, grab your guitar and play during commercials, or palm mute the strings and play while you watch your favorite shows.
I'll actually be continuously posting scales and guitar tips, so feel free to check them out, and hopefully they will help you. Good luck!