I can't comment on Clemson. I just wanted to let you know that I was initiated into ZTA at 28. Granted I go to a "commuter school" named Old Dominion in Virginia. But I don't know of age requirements for sororities.
Every sorority is different, as is schools. I just want you to know that it is possible to "older" and get initiated.
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ZTA
"Even in our sleep, pain which cannot forget, falls drop by drop upon our hearts. Until against our will comes the wisdom of God."