honestly no one really cares about age on backpacker tours. i did the NZ contiki and we had young and older mixing as if we were all the same age. but i must say it is not for someone who wants to relax. in NZ we had 5am starts and 11pm was prolly the earliest we went to bed. the friend i met on that tour did the Oz contiki and said it was the same. all breckies were included, no lunch and half the dinners were included in the NZ contiki. and you stay in hotel rooms with up to 3 other people. i did find it to be to much bus time. doing the north and south island in 2.5 weeks was a VERY big effort. i think the longest we were on the bus for was 10hours. and the shortest was about 5 hours. take your travel sickness tablets also cos oz is alot bigger than NZ.
