Reduce space between ticks in ggplot2 - r

Question

I made a time series plot of several random walks and by now I understand how to extract a certain part of it and how to change the ticks from years to months. But even after long testing I don't get how to manipulate the x-axis in my graph properly.
Right now, it displays 50 year-steps and only every second white vertical grid line is labelled (why? In every tutorial I watch all lines are labelled instead). What I want to achieve is to change the scaling, so less space is used horizontally (i.e. reduce the space between all the ticks on the x-axis), so the first tick would be at 2000, the second (not the third as is currently the case) at 2050, and so on. I think this should be somehow achievable with breaks, but I can't figure it out. Finally the plot starts and ends too early on the left and on the right, but I believe I can handle that.
Here is the plot:
set.seed(21)
n <- 2500
x <- matrix(replicate(20,cumsum(sample(c(-1, 1), n, TRUE))),nrow = 2500,ncol=20)
aa <- x
rnames <- seq(as.Date("2010-01-01"), length=dim(aa)[1], by="1 month") - 1
rownames(aa) <- format(as.POSIXlt(rnames, format = "%Y-%m-%d"), format = "%d.%m.%Y")
colnames(aa) <- paste0("aa",1:k)
library("ggplot2")
library("reshape2")
library("scales")
aa <- melt(aa, id.vars = rownames(aa))
names(aa) <- c("time","id","value")
aa$time <- as.Date(aa$time, "%d.%m.%Y")
ggplot(aa, aes(x=time,y=value,colour=id,group=id)) +
geom_line()

Answer 1

By default, ggplot adds a minor grid line (that is, a grid line without a tick mark or tick label) between each major grid line. To include only major grid lines add scale_x_date(minor_breaks=NULL). (If you're not seeing minor grid lines in the tutorial videos you've watched, my guess is that they are there, but difficult or impossible to see due to insufficient resolution and/or small size of the video image.)
To reduce the physical distance between tick marks, you would need to change the aspect ratio of the plot. For example, if you want the vertical extent of the plot to be, say 3", then you would need to shrink the horizontal extent until you get a small enough distance between tick marks. First, let's create a plot:
ggplot(aa, aes(x=time,y=value,colour=id,group=id)) +
geom_line(show.legend=FALSE) +
scale_x_date(minor_breaks=NULL)
Here are two examples of rendering the plot:
UPDATE: To answer the comment: For the plots above, I used grid.arrange to create the plot layout and then saved it as a png from the RStudio plot window. I used the widths argument to make one plot thinner than the other.
library(gridExtra)
grid.arrange(p1, p1, widths=c(0.6,0.4), ncol=2)
However, you can adjust the size precisely in many different ways, depending on what format you desire. For example:
# PNG format
png("wide.png", 500,500)
p1
dev.off()
png("narrow.png", 300,500)
p1
dev.off()
# PDF format
pdf("wide.pdf", 5, 5)
p1
dev.off()
pdf("narrow.pdf", 3, 5)
p1
dev.off()