We did TB Costa Rica too and it was great! Youngest on our trip was 2 (!) plus I think 4 or 5 in the 5-7 range.
Some of the parents of the younger kids were frustrated to not be able to zipline because the kids didnt want to do it.......If your 6 year old thinks it would be cool to zipline, I say go for a Costa Rica trip!
We have done a bunch of
ABD but not a pure Italy one even though they sound amazing in some ways - animal loving, thrill seeking DD doesnt gravitate to them. We did do Italy/Switzerland which was a really fun trip - not cities and museums and cathedrals. We also did TB Alpine Adventure which was great too - similar but different. (We love Austria and Switzerland!)
One of the biggest differences we find between TB and ABD is more grandparent/kid combos on TB (lots on CR and Alaska).