With my experience, with bikes up to 40 years old or more... They may be heavier, but in my experience don't require any more maintenance than modern bikes. I have replaced derailleurs long before they needed it, but for a good solid functional bike. The old 10 speeds (when 10 speed meant 2x5) are many times still rolling with the only maintenance done over the years being cables, chains, tires and bar wrap.

And when components need to be changed, there is always the option of upgrading to more modern and/or lighter components.

Admittedly, most 40 year old bikes that are worth riding have either been meticulously maintained, or have been sitting in garages for 39+ years...