Conditioning Matters Even More Now
I realize there are some differences between 25 and 40, and probably a lot of differences between 25 and 50, but not as many as you might think, especially if you have at least 10 years' worth of training experience.
But you can't train hard if merely pulling your pants on makes you wheeze. You need to do cardio or metabolic conditioning or whatever term you feel comfortable with. How do you expect to work hard if your lungs don't have the sass to carry on?
Moreover, your cellular batteries – the mitochondria – start to wear out, get lazy, take extended vacations in Cabo, or die as you get older. They need a kick in the pants so they get to multiplying, and that's what intense exercise provides.
Fear not, though, because you don't have to devote hours and hours to all that tedious, conventional aerobic training stuff where you sit on a stationary bike for an hour as your panini-ed prostate swells up to the size of one of those sand-filled Bulgarian bags.
Options That Don't Suck
At least three times a week, get on the treadmill, rower, or yes, stationary bike for a measly 10 minutes for some HIIT-style training. Focus on all-out efforts of 20 seconds, followed by 60 seconds of "active recovery."
On a treadmill, that might mean setting the speed at a leisurely 3 miles per hour and then cranking it up as fast as your little stubby legs allow for about 20 seconds, after which you'd drop the level back down to 3 again for a minute or two before you do another round.
You could do the same thing on a stationary bike or rower, or you might prefer short sprints followed by walking-recovery periods.
Alternately, you can crank up the incline on the treadmill to the Himalaya setting, or as high as it goes, and trudge uphill, Sherpa like, for 30 to 60 seconds before zeroing out again.
This type of training has been shown to increase mitochondria. That, coupled with the increase in endurance you'll experience, will allow you to lift as hard as you need to.