Hoggets are the name given to an old lamb or a young sheep, depending on how you look at it. Their meat tends to be darker with a finer marbling which is slightly strong and richer in flavour when compared to a spring lamb.
lamb but lambier
There are also other reasons to go for an older animal. Having more time out grazing means the muscle has had time to build up higher levels of micronutrients like iron, zinc and vitamin B, not to mention higher in protein and essential amino acid.
Much like other heavy and fatty meats calling for a fruit pairing, so does the pairing come of mint sauce and lamb. Not so much in the same way that mint is taking on the roll of a fruit but the sugar and acidity that is added to make a mint sauce cuts through the meat in the same way.