I feel so slow!!!

Today I did a nice progressive 2 mile warm-up and followed it by some nice stride outs ( or pick ups) Today's workout consisted of 4 x 3/4 mile repeats on 5:15 with 2 minutes of walking inbetween sets. So that averages out to be a 7 minute pace. After each interval I knew I had worked hard, it took about 45 seconds for my HR to completely recover so I figured, " no problem, go on the 2 minutes this is going to be easy", well, not so, it was hard, my heart rate climbed right back up after about 3 minutes and making it to 5 1/2 wasn't terrible but I was definitely working at the high end of my heart rate. #3 was the hardest, I think I slowed down a bit but I made sure I picked it up at the end to make up for my slowing down, interval #4 not the worst but I finished it. Cooled down and did about 7 1/2 miles total. Thank god over. Why do I do this to myself?

Why can't running be easier for me? I want to be so much faster and this is so hard. Will it ever come, did I just get into running too late in life? Is 41 too old to try to get faster? I'm not disappointed in myself with today, I did my workout, its just I want to be faster, really fast, and I just don't know if I will.