Too young, but I can see they being students inspired by one.
The thing that still gets me is the location of choosing. It isn’t a target by someone who hates the military, hates the government, hates any specific religion, hates ‘corporations’ or other targets.
It is a target of high visibility with a diverse population group. That is usually the type of target of Islamist. Shopping malls, buses, subways, Times Square etc. They go for visible and what will impact a variety of people.
An eco-terrorist would target a polluter or corporation.
An anti-government type would target some sort of government or law enforcement entity.
Occupy or something like them would target a big corporation or bank.
A nut like a Columbine attack would target something of meaning to them (this one is so vague it is always a possibility.).