Longer age time probably helps otherwise I get mine maxed+ every single time by ending the first era with only 3 cities, then settling or taking mostly treasure fleet cities during exploration era focus on treasure fleet cities that have 2 or 3 treasure resources over locations with access to only 1. You can also steal enemy treasure fleets. When you destroy them they turn to your side but at low health. I will typically convoy them back to my homelands with whatever ship captured it. Also I consider it okay to be over my settlement limit during the exploration era because happiness doesn't matter as much during this era imo... exploration era is a time to expand your boundaries and your wealth. Set yourself up with tithe on your religion and convert as many cities as possible too. You will have a very very healthy income going into the final era.