I've been running a Traveller game for our local role-playing group since last September. We started out with the characters as children using the latest iteration of my rules for children characters for Traveller. The old rules were published in Freelance Traveller. The updates I added bring the child character development more in line with other Mongoose Traveller classes. It includes Events, Mishaps, and Benefits for youngsters. Background skills are acquired as characters age.
I started or current game with a children's adventure, which went very well. It was a sort of "Three Investigators" or "Nancy Drew" style mystery. The party barely managed to find and solve the mystery behind the mystery.
All Grown Up
Once that was complete, we brought the characters up to 18. Then, depending on their relative ages, the characters got either 3 or 4 terms in standard Traveller careers.
Now we're well into the adventure. The group has a working starship and they just made their first interstellar flight as adventurers. They own one corporation, inherited from the eccentric old man of their childhood adventure, and they bought a second one on their first trip out of their home system. The second one was up for sale on account of 99% of its executive staff being suddenly dead. Probably just some paperwork error.
The party just sold 50 dTons of foodstuffs on an industrial world, and are backhauling lots of valuable food processing machinery. They'll be able to sell it for plenty, assuming the customer that the customer they have lined up isn't a smoking hole in the ground when they get back to their homeworld.
However, the party has started to engage in commerce in Traveller.
One of my players, new to Traveller, looked at me after the game and said, "So, basically, money is XP for Traveller. Right?"
I admitted that both money and equipment serve that role. After all, some things have a more than monetary value.