Got this for a 4 year old and it is certainly too difficult and fiddly a build for them - but I had lots of fun building the different models, so as a dad it got my thumbs up. At a guess 6 would be an ok minimum age to build without a grownup
The prop plane (on the box cover) is probably the most fun and pretty robust once finished
It is a great little set of lego and not too expensive. Once bored of the 3 models the parts can be used to build all sorts of plane/ helicopter type things though some of the many tiny parts may well disappear into the vacuum cleaner all too easily