Don't ever get discouraged. That is the only important advice.

Biking is awesome, and it's probably going to hurt at first. It did for me (my back and legs were SO sore), and I'm also close to your situation. 29 years old, just started a few months ago, 4 mile commute.

Before I started commuting, I was on my bike every day for shorter trips. Grocery store trips and riding for fun, mostly. It helped build strength and confidence, which is important becasue you don't want to get to work all sweaty, sore, and out of breath. Just KEEP BIKING. No matter what. You will improve.