There is no reason to wait! Seriously, if you have the money to buy it, buy it now. The price isn't going to go down. You're not going to "ruin it" by playing it before you're an expert. You
will learn faster, and be inclined to practice longer, on a really nice instrument, etc., etc.
People keep getting this whole thing backwards. You see people on Craig's list and eBay advertising cheap (and often inferior) instruments as "perfect for beginners" all the time.
NO! The perfect instrument for a beginner is the very best instrument you can afford to put in his or her hands. Old pros can play any old piece of junk and make it sound decent - beginners are often easily discouraged because they can't make sweet music and they mistakenly think they are the problem when the real problem is an instrument that is nearly unplayable!
Buying an entry level instrument, then a little better instrument, then a little better, then finally your dream is an extremely expensive mistake. Obviously, in some cases it's the only practical path if you just don't have the money to spare for a better instrument or you aren't sure you're going to stick with it. But, if you know you're sticking with it, buy the best instrument you can afford, then never look back.
Okay, I'll climb down off my soap box now...
John