Give up or Fight?

You are not too old! If this is your dream, don't let anyone take it away from you. There may be some validity to what those agencies told you. Change what you can, don't grieve over what you can't. I'm sure there is some other quality that you can accentuate. When someone says you're too short, you can say, "My legs are so slender, that they give me the appearance of being taller." You have to believe in yourself, or no one else will.