At 2yo I was told they are mature. 6yo is very old. About 20kg dressed.

A .243 is legal and perfect but a .223 will do it.

Euro skull mount is being done for me and posted home. Walked about 5 km but as they are territorial not hard to find. You just need access with country that has them. Lots of shonky operators will take you for a walk in empty country. Luckily my mates knew the right people and it didn't cost me a cent.