How old are you? You have until you're 25 (if it the day before your 25th birthday?) to finish so you can sign up and start the other sections and do the expeditions when you're ready. In my experience you have to be more mentally resilient than you think for expeditions. You will be carrying a lot of weight (so try to get fit and eat properly - not just on the expedition but in the weeks beforehand) for many hours then you'll have to put up a tent, cook a meal (potentially when it's pouring with rain), hopefully get some sleep, wake up early enough for breakfast, take down tent, walk more (and more camp stuff if you're doing silver or gold). All whilst being in a small group of people constantly.
I'm not trying to put you off. It's great fun. I did bronze and silver but had got more ill by the time I did gold and crashed after the first day of walking and felt awful that I couldn't cope. Even like 6 or 7 years later doing my silver expedition is one of the things I'm most proud of. But make sure you can cope.