maybe its fine for your age..
I'm 26 so its kinda hard to give advice..
but I personally would find 45minutes too much..

I'd go for a mile or two jog every 3rd day or so... that takes about 20minutes..
I hit the heavy bag a bit before i do my workouts at the gym, but thats just like 2-3 3minute rounds so another 9minutes.. n thats it.