Amazing hike
The hike starts at the Glen Alps trailhead, which has a very easy loop trail with a great lookout and view of the Anchorage area. If all you want is a gorgeous view of the area, that's the way to go. Very easy, short and flat.
The actual hike to Flattop starts at the parking lot area, and is well maintained in the summer. Our five year old made it all the way to the top. However, that said, it is very steep the last little ways, and not for pets or small children, or anyone with a fear of heights. The hike was a moderate challenge physically, but the views were amazing. A cow and two calf moose were spotted on the way. Beautiful!