At four months it's OK to top dress your coffee since in first year coffee requires 4-splits of nitrogen application of between 30-40 kgs/ha N and same amount of potassium also in 4-splits but very low or no phosphate at 1st and 2nd.year of growth.
One of the best fertilizer tailored for coffee in Kenya is NPK 22:6:12 +TE, please check out on this. Thanks