There are still very old trains in circulation on all sorts of lines in Japan, but I heard that 20-25 years is the baseline life expectancy for rolling stock. It is very good for business and for trainspotters.
Commuter trains in urban areas tend to be used upwards of 40 years with one or two rehabilitation cycles. That said, the busiest lines generally get new shiny trains every 15-20 years with older ones being sent to less busy lines.
The recent trend (since the 90s) have been to build cheaper, lighter and less long lasting trains, so that trains around that 20-25 year mark can be replaced with ones using the latest technology. That said, I've seen those trains being fitted with the latest traction units (not cheap!) around the 15 year mark, so we'll see how long they intend to use them.
With a pretty major possible exception on the Windsor-Quebec City corridor. Large fraction of Canada's population in a span of ~1200km. Particularly the Toronto-Ottawa-Montreal span with (metro area) population totally ~11 million over 600km, a Shinkansen-speed rail would be very competitive against air travel.
They're working on high frequency rail (which will also increase speeds to ~160km/hr), which should be closer to competitive, but still not great.
As an example, the model identifiers in use by the Paris Metro have the year of the _order_ in them and we still have MP59 trains running on line 11. They have been modernised and refurbished a few times, of course, but that's 63 years of service. Talk about a ROI.