Theres lots of different thoughts about this but what i write is just in my experience
i have 4 children, my first (now 11) started on abit of baby rice at just gone 11 weeks, my second (now 8) was about 14 weeks and my third (now 4) was 12-13 weeks i think, my fourth is only 10 weeks now and sowing no signs, i think she will be the latest one
health visitors say not until 6 months, it has changed to 4 months before but back to 6 months now but i believe when the child shows signs of still being hungry, so feeding more often but esp when they start waking up in the night again and cant go so long between feeds and also when they take interest in people eating
i didnt fully wean that young, it started with abit of baby rice, just a couple of mouthfulls once a day the increased it then fruit and veg purees
i always say go with ur gut instinct, its never failed me before, i strongly believe that us mums know whats best for our children