I had mine for 14 years prior to getting a CLI. Some combination of using it often, letting the balance post to the statement, paying it in full every month, and updating my income every month (even though it has not changed) worked for me and many others. I began receiving CLIs exactly every 6 months in June 2016.
Hi. Is this the MC or the store card? I too started out with a measly $300 limit with the Target MC. It took about 9 months to receive the first increase. They came rapidly after that. After 2 years, it was at $11,000. I do shop at Target a lot, and I pay it off in full each month.
Hope this helps.
Nov. 2013 FICO scores: EQ 565 | EX 536 | TU 539