Advanced set for 5.5 years old
I'm going to suggest that unless you're getting these sets at their retail price, don't bother getting any of these for a 5 year old. Instead, just get a current set, such as 31017 Sunset Speedster, which is still available at its regular price. Or check out the line of Speed Champions.

My reasoning is that a small child does not care about the vintage of a set and is not completing a collection, so any particular set is equivalent to any other. The sports car model is one that Lego refreshes every so often and there is almost always one available for sale, and you can usually get it at a discount. But all retired sets increase in price on the secondary market and I'd say you are getting zero value for your extra money if you hand this set to a child. They will love the set but not care at all if it's rare or hard to find.

As for how age-appropriate such a set is, it depends on the child. The Creator sets are fairly easy to build, usually. My 5 year old has little difficulty building them, though he has a fair amount of Lego experience. If your son has already built several models, these sets should be fine, even if the ages say 7 or 8 and up. I find that Lego's age recommendations are too conservative for my household, but YMMV.

Addressing your point about wanting to build with gears, etc. Most Creator models have minimal gears involved. Certainly the sports cars do not have working steering or anything like that. Creator sets almost never feature that sort of functionality except on the largest models. When there are moving parts, they are typically just hinged.

If you want something that features actual gears, steering, etc, you need to peruse the Technic line. Most of that is fairly complex. It's aimed at an older audience and I'd wager your 5 year old isn't ready for it - at least, mine wouldn't be. If Technic is too complicated, you might try one of these:

Fairground Mixer

Ferris Wheel

They are large models, fairly expensive, that feature both brick-built devices and mechanical movements. Both can be motorized by adding a motor (sold separately). Both are large sets that display well, but feature lots of play features. The Mixer, especially, is very cleverly constructed. I'd say both are too advanced for a 5 year old, but with a parent's help, and some patience, they should be possible.