Hi newgal,

I'm really into yoga, so you can think I'm a bit biased, but stretching those big muscles for a few minutes both before and after your workout is essential. That's why the professionals do it, every day, before they stress themselves. It ain't time wasted. Stretched muscles work better, and don't hurt! Sorry for nagging. [emoji202]
And... Becomes more important as one 'grows to maturity'! Speaking from experience.
In fact, I would say that getting this right, care of flexibility and mobility of joints, should be your primary concern, more than mileage. This will grow naturally. Just keeping injury free. Get that right. Run for ever! [emoji469]