While my personal preference is an older Peter Parker who is still getting fucked over by life but is still snarkily fighting the good fight, if they go with a young Peter, it's gotta be Dylan O'Brien. He's perfect.
I'd totes nominate Adam Scott for an older Spider-Man. If Paul Rudd can turn into a semi-serious criminal superhero, Scott can play a perpetually down on his luck nerdy superhero.
Probably would be pretty cheap too if he was game for it.
But honestly, I'd love if they just rebooted it and kept Garfield and Stone. Such phenomenal chemistry. And Garfield is a great Parker, just had a shit direction and writer.