I got my braces off in December and I haven't been wearing my retainer. Is it too late to start? (Photo)

Based on the photos you provided, I would say that the treatment time should not take more than a year to achieve a perfect smile. After all the spaces are closed, my recommendations permanent upper and lower retainers to prevent any shift of your front teeth in the future

If your retainer goes easily into place you should start wearing it again. Retainers are meant to be worn for a lifetime, if you don't want any movement of your teeth. If the retainer doesn't go easily to place you may need to see your orthodontist to have a new one made. Definitely don't just...

This process definitely should not have anywhere near this long. I have dealt with much more severe cases in the past (trust me, they were much much worse than yours) that have taken nearly half the time you have had yours on. It is time to get a second opinion.