for daily use and "as needed".

Daily dose is typically 5 mg for a healthy individual, and 2.5 mg for folks who respond at a lower dose or those with certain health risks or who are taking other drugs that may interact.  

The "as needed" dose is typically started at 10 mg every 72 hrs, and may be increased up to 20 mg every 72 hrs. Similarly, a 5 mg or 7.5 mg dose may be fine for those who respond to a lower dose.  

The other ED drugs (Viagra - sildenafil citrate; Levitra - vardenafil) both have shorter terminal half-lives (windows of effectiveness) of around 4-5 hours, while Cialis has a half-life of about 72 hrs. Cialis is also more selective for the PDE-5 enzyme (the target of action for each ED med), has a shorter onset of action (15 mins versus 30-60 minutes) and its absorption and effectiveness is unaffected by food intake - unlike the other two ED meds, which are significantly affected by timing of meals and diet. In quite a few studies, Cialis was chosen over either Viagra or Levitra by the large majority of patients who had tried more than 1 ED drug.

All of the ED drugs work the same, regardless of age. Age is only important to the extent that it often correlates with overall health and possibly concurrent medications.  

See your Doc, try it out

I took the 20mg dose about an hour before a session. It worked most of time but did literally leave me hanging on occasion. I asked my doctor about Viagra. He gave me the 100 mg dose. I used that for a while. Then started cutting it in half. It works great for me.

I found the side effects to be more severe with Cialis.

This is just my experience. Everyone is different. I'd say talk to your doctor.

Have been using 20mg for several years.  Its effectiveness has varied over the years, probably as a result of my fluctuating weight and fitness.  Fortunately, lately, it has been effective for 72 hours.  I put it to the test last week by seeing one lady on Wednesday after taking it on Monday for seeing a different gal.  (Reviews not yet submitted.)

Side effects are minimal for me.  When I can plan ahead I take it the night before because sometimes it seems to take several hours to "kick in".

Only "problem" is Costco's price continues to increase even though my insurance supposedly covers one-half of the cost.  In July I paid $21 per pill.