I happen to be a civil engineer in the 25-35 age group, and I am very fortunate because there simply aren't a lot of people in my age group competing to replace those 45-55 year-olds you mentioned. It's actually a little scary because civil engineering is a field where even a mediocre professional can be very successful.
Three engineers were debating the nature of God. Said the ME, "God must be a mechanical engineer. Contemplate the magnificent joints, sinews, and structures of the body." Said the EE, "No, God must be an electrical engineer. Look at the nervous system in all its intricate networks!" Said the CE, "No, God must be a civil engineer. Who else would run a toxic waste pipe through a playground?"
;-)