What is an appropriate age to start taking Finasteride? What are the side effects?

Hello and thank you for your question. Have you seen a dermatologist or hair loss professional? If not I suggest you do so in order to see what is causing your hair loss. You can take Finasteride but you need to see if that is the appropriate action for your case. Best wishes.Dr. T

There is no appropriate age to start finasteride. Patient have benefitted from age 18 - 60 yrs depending on kind of hair loss. Starting only finasteride is not the right treatment for androgenetic alopecia. It requires combination treatment to act on different pathways of hair loss. I would advise you to consult a certified dermatologist to evaluate your hair loss and then start treatment accordingly.All the best 
Dr Jyoti Gupta

I would recommend not starting it at all, and looking into alternative options. There are several known problems that exist when using Finasteride as a hairloss medication, lets take a look at each one:
Finasteride only works for a short
period of time.  It works for just a few hours a day (its half-life is 6 hours).Finasteride
does a poor job of
actually blocking DHT production. In fact, it only blocks 1 out of 3 types
of DHT receptors. That means hair loss is
STILL taking place while you are using the medication. This combined
with the short half life means that Propecia is about 60% effective at
stopping DHT from thinning your hair. Finasteride
is not customized to the
individual. Like millions of Big Pharma medications out there, the exact
same dose of Finasteride is given to people who have different heights,
weights and
biochemistry. This means that men who want to stop hair loss for good
can take the recommended
dose of Finasteride every day, and experience nasty side effects for no
good
reason! While for other's their dose may be insufficient to even reduce
DHT by the 60% it is rated at.It
is also worth noting that any medicine that actually can make changes
inside your body, are required under the FDA to be available by
prescription only. This therefore means that it is not possible for
anything that does not require a prescription to cure or prevent hair
loss or regrow thinning hair. Thus, a personalized medicine will be the
best choice because instead of a "one size fits all" approach, you will
be taking something which is truly catered to your body's needs.

The number one first step I recommend is a
comprehensive consultation with a hair regrowth specialist who will
perform lab tests to determine  the underlying cause of your thinning.
Without labs, no-one can really know what your true cause is and any
treatment will be temporary at best. From here, you can receive the best
treatment for your case.
The treatment is out there. Good luck on your search.