My first commutes were age 52. The full commute distance was 35 miles round trip, which completely destroyed me. I was not a strong cyclist and the hills were a struggle.
I started with partial commutes, drive to a safe parking lot 1/2 of the way to work; then bike the rest of the distance. I also did not commute every day. On Fridays I worked up to a full commute when I had a shorter workday and a weekend to recover.
20-30# in the panniers is a lot. Do you really need all that stuff? I was able to keep the bike cable/lock on the rack at work and do not take my laptop home from work. Toiletries are rebottled into travel-size containers. I keep a pair of shoes and some sweaters at my desk so I don't have to carry big/bulky items back and forth.