Volosong, I am 56, and I've been riding my fixie pretty exclusively since october of 2000, when I got it. It's a Gunnar Street dog, that I had built up at Harris Cyclery.
If you are a cyclist in decent shape, (i.e. you ride on a regular basis) you will not have any problems. Yes there is a learning curve, and it varies from person to person.
You might get sore in a few places where you didn't before, but this passes. Before long, you will probably be doing what I do now: Taking vacation days to go riding.
It is quite addictive. You'll find yourself becoming a better, more fit cyclist because of it.

If it is conversion you want to do, some shops, Harris for one, specialize in doing them, and can guide you through the process if you want to try it yourself. The late, great Sheldon Brown favored 70s road bikes for fixed gear conversions.

Do not fall into that 20-something business about going brakeless! It is foolish and against the law. No idea why they insist on doing this. Making a political statement about the human condition, or some such useless glop.

I run toe clips and straps. No apologies, further discussion not required. A cycling computer? I blow that off too.

My gearing is 42x15. This works out to about 75 inches. This is fine for me, and gets me up the hills I encounter with ease. If you live in very hilly country, you might want to try something lower.

Welcome to the rebel side.