When I buy fresh yeast packs from my LHBS they're usually less than two weeks old. I'll do a 2 L starter, and pitch at high krauesen to a 5 gal batch. If I'm using saved slurry which has a higher viable yeast count per ml, I'll do a 2L starter and split it to two 5 gal batches.
This is a process I've adopted in the last year or so after years of more anal yeast prep. I always religiously followed the calculator on brewersfriend.com and made big stepped starters which I'd let finish and decant before pitching.
With the new process I'm getting a lot shorter lag times and seeing great finished results. Thanks to some of the guys on this forum for convincing me to try this approach!
edit: starter temps are not really all that important. Warmer within reason is better because it will encourage yeast reproduction which is what you're doing, not creating beer.