Africa is less than a century out of independence from various European powers.
Using colonialism as an explanation for lack of economic progress isn't supported by the evidence. The African country with the longest and most pervasive colonization was South Africa. The country with the least was Ethiopia, which maintained its independence except for a few years of Italian control in the 1930s. Yet South Africa is near the top of the African economic pile, while Ethiopia is near the bottom. There are plenty of other examples. Countries with long periods of colonization, much interaction between the locals and the colonists, and lasting European-style laws and civil institutions, are doing far better than countries where colonialism was less influential.