Present perfect

Hello,

Could you check these sentences, please? I have underlined my choices.

How sad! George (dream) dreamt of going to California before he died, but he didn't make it. He (see, never) never saw/has never seen the ocean.

Jonny, I can't believe how much you (change) have changed /changed since the last time I (see) saw/have seen you.(Is the 'since the last time I saw you also possible) You (grow) have grown/grew at least a foot!

This mountain (be, never) has never been climbed/was never climbed by anyone. Several mountaineers (try) have tried/tried to reach the top, but nobody (succeed, ever) has ever succeeded/succeeded. The climb is extremely difficult and many people (die) have died/died trying to reach the summit.

I (visit, never) have never visited Africa, but I have traveled/traveled to South America several times. The last time I (go) went/have gone to South America, I (visit) visited Brazil and Peru. I (spend) spent two weeks in the Amazon, (hike) hiked for a week near Machu Picchu, and (fly) flew over the Nazca Lines. (I used present simple with every verb)

I (have, not) have not had this much fun since I (be) was/have been a kid. ('Have been' would be also possible, I think)

Thanks