Six got you feeling a little less than good? Lightweight.
It's age, mate. I used to go out and drink 10 pints, no worries at all. Changed when I was in my mid-late twenties. Now, even 4 pints can be a bad idea on a work night. Usually 5 is fine, 6 is dodgy midweek and 7 is a definite mistake.
Yeah, I don't know if you're old enough to blame it on age.