That's a new definition then, because for millennia morals were derived from exactly those "externally enforced behaviours": from religion, society, culture, etc.
The personal codes someones makes on their own can be anything and everything ("shit on everybody to get rich" is a perfectly valid code that millions use). Nobody would call that "moral" though -- because precisely morals are those beyond the individual whims (though whether an individual follows them its their choice).
Personal principles someone follows are only fit to be called morals if they follow an extended, external, moral code. Which might change over time, and be culture-specific, but it's not "whatever I say".
As far as one can tell, social animals show something equivalent to morals in every experiment we can devise -- and in the vast majority of cases, it is not a learned trait (elephants being the best known counterexample in that their cultural norms and morals are indeed learned).
We can't really experiment with humans, but the few experiments that have cleared ethical committees, it appears that babies as young as 6 months have a sense of equality and justice, see e.g. [0]
Externally enforced behavior is not "morals".