I used to ride bicycle to school when I was in middle and high school, and I havn't been riding after high school until now, over 30 years later, so this is considered getting back into bicycke riding again. About this Fallen Leaf Lake trail, there were many climbs and breaks for me to get there, and also my bike came with the Shimano Alfine 8, so the gear range is limited to only 8 gears, for high-hills climbing it is bit of challenging for me, there were a few times wanted to quit, but I told myself just keep going, when the hill is tough just climb as far as I can, then stop for a short break, after 3 or 4 small break and water intake, I found myself at the top of the water fall, so I made it, this is the first bike climb of my life and by making it to the top, it gave me some confident now to tackle the next trail soon. Oh I forgot to tell you that I did get in to many dirt single track sections but there were so much rocks and the technical there is not for beginners for sure, so I walked my bike along the hard parts and find my way out to the pave trail to continue to the top.
Now I think that if a beginner can make it for the first time ever, most people should be able to do it. Lake Tahoe is the biking heaven, so it does not matter which trail you are going to try today, it will be as beauty in its own way, so just do it, don't stay in the house, go out there and hit the trails.