We have learned that our 2 kids do better together when we aren't with them. They are a team when left alone, but tend to bicker when a parent is around for attention.
We left them alone at the resort for the 1st time last year. They had been staying home alone (together) for about 8 months prior. DD was almost 13, had been babysitting since she was 10. DS was 9 1/2. Rules were spelled out ahead of time, no leaving the resort and they must stay together at all times. We had an early tee time, they slept the first couple of hours we were gone. The rule was they were to call when they woke up, and they did. They grabbed breakfast, bought a small bucket (we were at BC) and then spent time building sandcastles together (I swear there is no way they would have done that together if we had been around!) and called to ask if they could go to the arcade and use some of the money leftover from breakfast. They had a blast that day. Did it again twice this summer (once while we were in signing the papers on our
dvc purchase & once to play golf) and they thoroughly enjoyed exploring SSR on their own.
Now one night DD wasn't feeling well when we were at the Studios and wanted to go back to SSR by herself and we wouldn't let her. We weren't comfortable with that, however if we had been staying at BCV or BWV we wouldn't have minded her getting on the boat to go back. It was the bus issue that worried us.
I know kids that couldn't or wouldn't want to be left alone at 14 years old. My kids are very independent and responsible. In the end, I think it really comes down to the children involved and each parent knows their child best.