Congratulations on your new boyfriend!
Without knowing you, or your family and friends, it’s hard to know what they mean by “age appropriate”; but it does sound a little like a code phrase for something else.
You may be on to something when you speculate that it means someone who makes more money than you. Often, the older partner in a relationship is presumed to be contributing to the financial support of the younger partner, especially if the age difference is more than a few years. And your family and friends may feel you’ll be better off when you’re somebody’s boy toy, rather than somebody’s sugar daddy. So they encourage you in what they feel is an “age appropriate” relationship. (They also may not be fully aware that they’re thinking this way; I think it’s kind of an age-old bias.)
Of course, this is all just wild-ass speculation on my part. You might test out the hypothesis by dating a younger guy with lots of money, Ryan Phillipe for example, and see what your family and friends have to say about that.
Just don’t lose hold of your main squeeze!