I'm 22, been making comics since I was really little (like elementary school, I have several comics of like Digimon parodies, Pokemon/YuGiOh/Sonic mash ups, etc), however I started taking on drawing as a serious hobby around 7th grade, so I'll use that as a benchmark and say about 10 years. As for seriously making them though, I'm just about to get started~
The project I'm going to be working on is actually an original story that I started developing way back in 7th/8th grade, but never made it past chapter 6 with (in writing, I've only ever drawn as far as CH 2), so I'm really excited to both revise it (my story telling capabilities have vastly improved since 7th grade haha) and actually develop it. : D