You have to make a subset of the data that contains the years you want to plot. There are many ways to do this. Let's say your data are in a data.frame named DF and you have a column named Year. You can select for the years up to 1990 with
EarlyYears <- DF[DF$Year <= 1990, ]
Or you can use the filter() function from the dplyr package.
EarlyYears <- filter(DF, Year <= 1990)
You can then make your plot using the EarlyYears data frame.