Go generalless.
With 75 provinces your empire should be awash in gold. So just let your 45 year old be a fat cat, preferably in a city with a fertility temple. Send out the legions with lots of +morale units like prima cohors imperatoria or mercenary generals, naked spearmen or whatever and superior high morale units so they won't route. Hire morale penalty mercs like wargozes and tindanotae. Victorious armies will sometimes spawn men of the hour who you immediately retire and put out to stud in some city doing no military service, just procreating and let the legions win without generals. Sooner or later you should get a decent kid, let him govern a city with a war temple until he becomes hale and hearty then let him go out and crush the world.