Even if he seems 'ready' (grabbing food isn't a good sign of readiness though as all babies should be grabbing things by about 4-5 months), there are good reasons to wait until 6 months. One being it gives him more time to hone his hand-eye coordination, meaning it will be even easier for him to feed himself, and he'll be even safer because he'll be able to sit up better by then, even if he's doing it some now. The better they can hold themselves up, the less likely they might be to slide backwards, which can make them more likely to choke. Plus, at 6 months, you can feed finger foods (like that apple) plus wheat, oats, dairy, meat, etc., more than just pureed veg and fruit, and those are much more exciting and calorie-dense foods anyway, when also paired with fruit and veg. He will also be more likely to have lost his tongue thrust reflex by then (meaning less refusing food or gagging because it's so sensitive), which will make mealtime more enjoyable for both of you.
Plus, weaning is a lot of work. It's so much easier when all you have to worry about are milk feeds and not preparing or storing or transporting solid meals, even if you do BLW like we did (meaning he just eats what you eat). You still have to make adjustments in preparations to make food safe for a baby to eat and some days you may find yourself cooking two completely different meals, if the one you're making for yourself isn't 'baby-friendly'. Weaning is fun and great, but it is work. If you can put off having to worry about food for another month, I'd do it. It will be here before you know it and you'll be glad you waited.
