Might not be quite "hard" enough, but perhaps try the Interdepency trilogy by John Scalzi.

Such a great movie. To add to the list...

It's Mega Maid, sir. She's gone from suck to blow.

Light speed is too slow. We'll have to go right to Ludacris speed.
Ludacris speed?!?
What's the matter Colonel Sanders? Chicken?

Nothing wrong with being in school with a more mature outlook. My first run at college, I pissed away a sweet academic scholarship and ended up dropping out after sophomore year. When I went back at 26, I was more prepared to put in the work and focus on what mattered (getting that degree). I basically had to start my college career all over, and while many of the general education classes I had to take were predominantly filled with younger students, the further into my program I got, the more post-bac and non-traditional students I encountered.
I let it bother me at first (felt like a failure, yadda, yadda). When I got over myself, I had a great time learning. I wasn't there to impress anyone - I was there for me. So you do you.

Currently reading "The Kaiju Preservation Society" by John Scalzi. Lightweight, humorous sci-fi. Just recently finished "The Gentleman of Moscow" by Amor Towles, which is lovely storytelling if you enjoy character building. KPS is definitely a much different feel.
Depending on what you like to read, I would recommend both - but for different reasons.