Are you talking older as in high school or older as is out of high school? It depends on how hard you are willing to work and how much flexibility you already have. My suggestion would be to start taking privates so you can work one on one with a coach who can see all your weaknesses and strengths so you can build on those.
I just started tumbling, and I am in college. I also coach a group of adults (ages 20-37), some with prior tumbling experience, some with none at all. They are all progressing. Right now, i am working on my back handspring and I can do the basic back walkover, and i can front handspring on the floor....It's definitely possible.
I am 24 and only can do a round off, I am hoping to have backhandsprings inless than 6 months and hopefully standing back tucks. I am going to start taking privates this weekend, but it is expensive so I'm not sure how quickly I can learn, I am more afraid than anything. I don't want to get hurt!