I'm in my 30's. It's absolutely normal to feel exhausted by hiking if you haven't done it or other sports in quite some time. In the hiking groups I used to a

I'm in my 30's. It's absolutely normal to feel exhausted by hiking if you haven't done it or other sports in quite some time. In the hiking groups I used to attend, there were plenty of people decades older than you who could go much further than 5km without a sweat (figuratively speaking). I imagine that if you do some hiking periodically that your body will adjust to it in a short period of time.