They can have weetabix from 6mo. I tried it with my son then but he wasn't keen on the texture. Tried again recently at 8mo and he really liked it - esp with half a banana mashed in.
A good tip is to heat the milk in the microwave for 40 secs before adding the weetabix to the bowl and smushing it up - it makes a kind of smooth porridge that way which babies seem to like.
Fwiw here's an average day for my 8mo:
Breakfast: 1 weetabix with whole milk and half a banana. Or a small bowl of cow and gate baby horrid he followed by half a slice of toast with peanut butter,
Lunch: half a roasted sweet potato all mashed up wit cheddar cheese followed by a fruit pot (those pots of fruit purée sold everywhere - organics or cow and gate or whatever). Or 1 egg scrambled with a bit of grated cheese mixed in and 2 toast fingers. With same fruit pot pudding.
Dinner: whatever we had the night before, reheated and blended to a purée (with rice or baby pasta shapes added where appropriate). Recent examples include: fish pie, homemade chicken korma with rice, homemade spag Bol, shepherds pie etc etc.
He also quite likes: oven chips (has had a few off my plate when he refused his pureed dinner!), psi au chocolat (occasional breakfast treat), eggy bread/French toast ditto weekend breakfast, half a hot cross bun with butter as a pudding, small pot of ambrosia rice pudding, the occasional Ella's pouch when out and about....