My monstera put out its first split leaf after 2 years and 4 months of waiting
I got a tiny monstera deliciosa from a plant swap in Austin back in spring of 2023, just 3 sad little leaves in a plastic cup. For the first year it did almost nothing except drop one leaf and grow two more boring heart shaped ones with zero splits. I moved it from my north window to a spot 4 feet from an east facing glass door last July and finally gave it a chunky mix of orchid bark, perlite, and potting soil instead of the dense stuff it came in. Two weeks ago I walked past and there it was, one new leaf with 4 little fenestrations, and I actually yelled. Now I'm wondering if the light change did it or if it just needed to hit a certain age, because I have a friend in Seattle whose monstera is way taller than mine and still has no splits at all.
Got to disagree that age is the main thing here. I've seen monsteras throw fenestrations at a year old when they get strong light, and I've seen 6 year old plants with zero splits stuck in a dark corner. My guess is the move to that east facing spot plus the chunkier mix did most of the work, since light drives the energy for bigger leaves and the bark mix keeps roots from sitting wet. As for your friend in Seattle, tall does not mean happy, a stretched out plant reaching for a dim window can look huge and still never split. Give it a couple more leaves and you'll probably see the splits get bigger each time.