I seem to produce wacky babies who don't need sleep, but both mine stopped napping around 18 months. I had the same problem - if they napped they were up late. It took about a week to adjust so they weren't melting down at supper time then they were fine. I think I did make their bedtime earlier while they were adjusting. Some kids have much lower sleep needs. I remember being so upset with DD1 when she dropped to one map at 8 months...I thought she HAD to have 2 because the books all said babies that age needed two. LOL. I say drop the nap for a week and if it's miserable,, implement it again but maybe shorten it.
This is my babies to a t. I enforce a quiet time every day but they don't sleep. They get to have a movie on for quiet time and it is over when the movie is over. It makes it easy for them to judge the time and not keep calling for me to ask if they can be done. I try to pick long, boring movies.