Nothing is stopping you from doing this. A lot of people start out like this. Either using just headphones, mono out to something like a keyboard or bass amp, or monitor style speakers connected to the headphone out of a synth.
To connect a 1/4" TRS headphone port to separate monitors as you describe, you’ll need a male TRS to dual TS female adapter, and two TS cables. Keep the monitors at 0db, and adjust the volume using the headphone volume control on the synth.
However, one thing I’ll say is you will likely get bored of that setup pretty quickly. With no effects or eq, the raw sound of the synth can become fatiguing on the ears very quickly. I’d recommend the next step as either some type of multieffect or a mixer with some stereo effects. Overdrive or distortion, chorus, delay and reverb should be a great start. The mixer is for when you want to add a drum machine or second synth 
Personally, I started on a microbrute connected through effects pedals to a guitar amp. But very quickly realized that was not going to cut it for long.
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