Is Finasteride effective in men older than 35?

Yes, Finasteride is effective for any age. it does not matter if you are  35 or 45 you will see its effects.

Yes finasteride also effect after age of 35 ..But you may have Post-finasteride syndrome, occurs in men who’ve taken finasteride to treat hair loss by a chance of %4-5. That may causes some symptoms include: loss of libido, erectile dysfunction, depression, panic attacks, gynecomastia, muscle atrophy.

Yes, it can be, but side effects are often not desirable. ED is one of the less desirable. I suggest you seek out a good Functional Medicine or Integrative Medicine or Anti-Aging Medicine physician. They are generally very good at managing the hormones without the adverse side effects. 
You may also want to consider regular PRP treatments (6 month intervals) if hair loss is just beginning. If more advanced, you'll need to start with a regenerative program followed by maintenance treatments.
Doing the above will likely improve not only your hair, but other issues life at 35 and above throws at us.
Wishing you all the best and wonderful solutions.
Warmly,
Arbella Sarkis, MD