Well, first, welcome back.
I guess it's always a good thing to check with your doctor just to make sure (I did a blood check recently as well just for that reason). Age would really matters if we were speaking of menopause, but the mid-twenties aren't exactly a period when your metabolism drops all of a sudden and causes you to pack on weight quickly, at least not if your lifestyle doesn't undergo drastic changes as well--even if it's true that we're starting to slow down slightly all the same after 30-35, and then later on too, of course.
As for your question--I'm 28, and no, I haven't been experiencing that. I started doing things 'seriously' regarding my weight when I was about 25 1/2, and every time I've been 'mysteriously regaining' in between and before that as well (I had lost weight first around 18-20, though I never reached a goal, nor had any), just looking back on it with an honest eye makes me realize that it was only my fault for having let myself fall off the wagon, if I may say so. To me, age hasn't become a problem yet, the major problem is lifestyle and getting caught up in bad routines. But our bodies are all different in that regard, so probably one person's case isn't very representative.