Should I travel to Morocco alone as a young female?

All of the city centres in Morocco's metropolitan cities are basically as safe as any other city. Tangier, for example, has cleaned up its act a lot. Most safety tips are 'generic' non-gender specific, like stay alert when using an ATM or walking on poorly lit streets after dark.

A few tips pertinent to women, however, are...

Train and bus travel -

Traveling by train or long-distance bus is generally considered safe, though it pays to keep one eye on your luggage at each stop. Women travelers should look for seats close to those occupied by Moroccan women. The country’s taxis— both petit and grand—are considered generally crime free, but may be poorly maintained and driven recklessly (a request of “beshwïya” [“slowly”] may or may not be heeded). Traveling on a crowded city bus can be unsafe.

Harassment -

Encountering unwanted attention from Moroccan men is unfortunately a possibility for female travelers. The relative lack of social interaction between the sexes in Morocco results in men having little exposure to women other than their immediate family. They often see Western women as not being bound by Morocco’s social restrictions, and perhaps have a not-so respectful assumption of them via easily accessible Internet pornography. This assumption of availability emboldens the Moroccan male to make advances on female travelers that they would never attempt with Moroccan women. This generally takes the form of catcalls and straight-up come-ons. Blonde women may be singled out, and women traveling alone generally receive more attention than most. Women on the receiving end of nonphysical sexual harassment should do what Moroccan women do: Ignore it. Showing confidence and self assurance also seems to deter a lot of would-be Romeos.

Dressing modestly —

a long skirt and loose, long-sleeve shirt—can help. Having said that, I’ve seen Western women wearing jellabahs (the traditional robe worn by local women) on the receiving end of lewd comments.

A generic tip on the grands taxis -

There are some pertinent safety concerns attached to traveling in grands taxis. Many drivers are under pressure to work long hours, and falling asleep at the wheel is a definite possibility on night drives, so it’s best to travel by day. Within that busy day, a driver is trying to fit in as many journeys as possible, and will often drive as if there is no one else on the road. Overtaking on blind corners is common on many grand taxi journeys. Added to this is the lack of available seat belts, because it’s either too cramped within the vehicle or there quite simply aren’t any. Needless to say, when chartering a grand taxi, stress on the driver your expectations toward his driving.

Hustlers, Faux Guides, Pickpockets, etc - MeNoTalk's comment above applies. If someone is trying to distract you, go into hyper-alert mode. This holds true for both men and women.

Frommer's Morocco (ISBN 978-0-470-18403-5) has these and several other valuable tips. It's recommended. Citations from Google Books