Updated November 26th: read my full review of Banjo-Kazooie here

Sum up:
Banjo-Kazooie: Nuts & Bolts is a sequel to the N64 platformers of the same name. Nuts & Bolts has the same characters and core gameplay of the previous games, but with one distinct difference: vehicles. This time around, 20% of the game will focus on classic platforming elements, but the remaining 80% will be made up of using fully customizable vehicles (choose from over 1600 parts to create anything from a helicopter to a speed boat) to traverse the game's levels.

Like previous games, Nuts & bolts will have a fully explorable overworld (which is roughly 16 times larger than before) that branches off to the game's many levels. The game also includes an online and offline multi-player mode (where you pit your custom vehicle against other players), and co-op mode (it's however, not a full campaign co-op, meaning you only play as a team on multiplayer).

Recommended age:
The ESRB rated this game "E10+" for Everyone 10+, listing "Cartoon Violence" and "Comic Mischief." Both of these descriptors are also listed in games like "Super Paper Mario" and "Super Mario Galaxy," meaning this won't be any more extreme than those mentioned above.

However, from what I've seen of the game so far, it does seem that kids 7- might have a few difficulties with the button setup and some of the gameplay mechanics. But even if there's a moderate learning curve, you can take your time practicing in the overworld (or just play around, it is huge). But overall—because of it's sheer complexity—I recommend this game for ages 10+.