I'm 53 and have been cycling for about 5 months. I've got a Trek 2.3 and have worked my way up into the 80 - 100 miles per week range. I lazily roll in the low 15s on my daily commute of 13 miles round trip. In a pace line I can ride 16 - 18 MPH for 50 miles on the flat. My commute is dead flat and I'm looking for a better workout from this commute. It appears a fixie would be a much better workout but I didn't want to assume anything. My commute is functionally traffic clear and on very smooth roads.

Am I thinking correctly about the workout?

My other reason for being here is a bad case of N+1 mixed with "clean" envy. I just love the lines of these Fixies.

Thanks!