I started Dylan on solids at 5.5mo - he was almost 18 pounds at 4mo
FWIW, an ebf baby feeding twice a night at 5mo is completely normal - breastmilk is much more easily digested than formula and ebf babies in general need to feed more frequently and need night feeds for longer.
If you're wondering whether your lo is ready for solids, have a read here:
http://babywhispererforums.com/index.php?topic=36922.0 Just remember that solids shouldn't replace breastmilk/formula
Up until 1yo solids are just for fun and learning, and it is milk that provides all the nutrition, fat, and calories that they need.
If you're going to start, current recommendations in Canada are to start with rice cereal - it is unlikely to cause an allergic reaction and is fortified with iron. However, it can be really tough to digest and cause gas and constipation. Mixing it with breastmilk can help, but rice cereal was tough for us. Tracy recommended starting with pears - they are mild in flavour, easy to digest, and also unlikely to cause a reaction. People worry about babies developing a taste for the sweetness of fruit if introduced before veg, but with breastfed babies they are already used to the sweet taste of breastmilk.
hth