I'd lean to aggressive. Set the barrier high and go for it. We bought our first road bikes in the early 70's. Pokey. Got race bikes in the mid 70's. Much more fun and therefore motivational. But, due to lifestyle/job, only rode 6 to 12 times/year. Retired in '98, three/four years later got more serious at biking and we now typically ride twice per week emphasising longer rides. We always have gone for the sporty bikes --- suitably geared for our more limited bike fitness (and age) as we do other stuff as well.
At 72 I have no problem with a 45/50 degree back angle (much lower on steep climbs on the trails), 80 to 110 cadence, and rideing in the heat/cold, etc. It's all attitude. Folks have a tendency to see age as something to blame for being timid or for pains due to lack of use. Like being over-50 was some how a limiting factor.
The wife, 70, lusted for this used 18 lb carbon race -configured 30 speed road bike a few weeks ago. I thought it was a very bad idea as I don't even like that kind of bike. But, if it makes her ride more and harder, it's worth the big $'s. Had to change out the ultegra drive train for a mountain bike drive train (works fine with STI) or she'd never make the hills. She can climb with a 22/34 now when she has too just like her other two bikes.
Al