Can nucleic acids, proteins and starch be considered as step growth polymers?

Yes, nucleic acids, proteins and starch can be considered as step-growth polymers.

Step growth polymers are condensation polymers. Monomers which possess bifunctional or trifunctional functional groups can combine by the loss of a simple molecule like water, alcohol etc. leading to the formation of polymers having high molecular mass.

For example, DNA(deoxyribonucleic acid), proteins and starch all are formed by removal of water molecule when their respective monomeric units join together.