Density should be based on what the density you have on the sides and back not your age.
If for example your side hair resembles 60% but around 70% at the back then try and go for 60% and slightly lower on top,maybe 50%-55%, and 65%-70% for the back that way it would be perfectly natural to look at.
Don't think that density is age related as this is a very common mistake made by newbies resulting i something that just screams wig!!