It sucks that Propecia didn't work very well for you. I feel like I have a similar case. I took Propecia when there was no noticeable difference in the thickness of my hair. I've used it for 10 months, and it became very diffuse during this time period. I also suffered major sexual side effects, which really put my down.
I've since switched to Avodart on December 2, 2005. I still take it once daily, with a hot cup of Lipton's Green Tea-- on an empty stomache.
I haven't suffered any side effects whatsoever, and it seems to have stopped any shedding, reduced itching, made my skin clearer, etc.
(Knocking on wood during this entire post)
I have only gained positives from my experience with dutasteride. I'm very happy I made the switch. I just think that my body exemplifies a textbook case of DHT negatives-- hair loss, bad acne, unclear skin, lots of body hair, etc. etc.
I have a strong genetic disposition to go bald early-- my older brother is 23 and already has the dreaded island, and is going bald without a doubt. Of course, he hasn't gotten started on any treatments, either.
I think that Avodart might be working where finasteride failed for me.
There is the possibility that if you take Avodart, you might get side effects. If this is the case, you can always get off Avodart, and the side effects will eventually go away. Don't be scared to take Avodart under the supervision of a doctor.
Will dutasteride age your skin faster? In all liklihood, no, it won't. In fact, because less DHT is in your skin after taking Avodart, it's likely to have the opposite effect-- improving your skin.
Cancer? No, the four-year test results from dutasteride show it's a safe drug to use in the long term-- with all sexual side effects almost diminishing with time. (whether still taking Avodart or not)
Alzheimer's Disease? No.
I would talk to your doctor about it. Maybe get some simple blood tests taken every once in a while, then be on your merry way.
Who knows? Maybe Avodart can work as well for you as it does for me.
Best of luck, please feel free to ask any more questions.
Andy