You know, just earlier today out of curiosity I made a small spreadsheet calculating my available CLs + some other parameters (overall util, debt-to-income etc). Apparently, with income similar to yours (~55k) and length of my credit history of a little bit more than a year I currently have ~23k in available credit across all cards and I doubt I reached my overall limit. 

Just as a kind of benchmark - one of my relatives with 150k-ish income claims to have around 100k in available credit on cards (not including home equity lines etc) in addition to mortgage and auto loan. He has spotless history of 15+ yrs as far as I know.