We actually climbed up part of Ben Nevis this morning! Went up the rocky section near the Youth hostel which was fairly steep, and then the gentler route back down the visitor centre.
What surprised me most about this area is how variable the weather is, one minute it looks lovely, the next it’s raining (no heat wave here!), so be prepared for all weathers. Wear decent walking shoes, layers, waterproof coat etc. Also, make sure you have plenty of water, food, snacks etc - it’s amazing how a chunk of chocolate can boost you. We were amazed by how casual some people were dressed.
Also be prepared for how long the walk will last, one sign we read said allow for seven hours (four up and three down).
However, whether you make it all the way up or not, the area around here is stunning.
incidentally, if you have a teen, you may consider visitiving Glen Etive, Skyfall country, or Glenfinnian viaduct, as featured in the Harry Potter films.