Assuming that at age 70, you have lots of time to do what you want: yes to riding more hours -- and yes to riding more often.
I just "aged up" to 65 this year, and I'm trying something new: I'm simply putting in more hours on the bike, almost all at an easy/moderate pace. It's working, I feel "mid-season" strong.
With the less-than-great weather, I haven't been doing any long climbs. But the short, low-elevation hills are feeling pretty easy. I tried a full gas effort on a short Strava uphill segment this week, and I managed a 3rd place time. Not so bad for a senior citizen.
So here's the training that's worked for me:
- just put in the hours on the saddle at easy/moderate pace
- ride at least 4 times per week
- try some harder but short efforts, no more than once or twice per week
- start adding in longer tempo climbs as the season progresses