Hi! You can try the code below:
library(xlsx)
write.xlsx(Top_Balances, "April Aging.xlsx",sheetName = "Name1")
write.xlsx(Over_60, "April Aging.xlsx",sheetName = "Name2",append=T)
write.xlsx(CI, "April Aging.xlsx",sheetName = "Name3",append=T)
write.xlsx(CL, "April Aging.xlsx",sheetName = "Name4",append=T)