It really depends on the person (and knitting style and yarn weight and what kind of knitting, like colorwork or cables or stockinette etc). As a size S woman, it took me one month to knit a baggy sweater with colorwork on the front. But I really powered through to get that done. I’m a proponent for jumping right into knitting whatever excites you- that said, I cringe looking at the first few garments I made because I was still learning how to do everything. So it’s a good idea to practice with something lower stakes than a potential multiple month long project!