The Horror Of Immortality in anticlimatic

If granted immortality at, say, the age of 35- assuming also that the speed in which it feels time passes us by continues to accelerate at the same rate that it does for our first average lifetime or so, how long before everyone in your own generation ages and leaves you, followed by everyone you knew even as youths in your first 100 years, and then how long until the birth and death of a human being feel almost instantaneous, anything and everything occurring in their lives redundant and irrelevant to you, rendering any further association with humanity impossible- and how long could anything that may have once been human exist alone like that?