I’m baffled as to why people think Simms hasn’t got any pace already. At every level he’s played at , including League 1 , he’s outpaced defenders to score his goals. You wouldn’t play him as a winger, but I’ve never seen anything yet to doubt his speed through the centre, I can’t recall any defenders who‘ve beaten him for speed. It’s all relative of course, he’s been measured against U23s and League 1 defenders in the pace stakes.
Re your “ Their pace is their pace” , That’s only partly true , if a player is slow at 20 he’s not going to be a speed merchant at 30. But in the world of athletics you don’t usually hit your peak as a sprinter until 24- 30 years. There are many physical and practical reasons why a 20 year old will get faster, particularly as their bodies develop with greater training load . Simms could get faster with specific training, but too much and it would likely come at a cost in other areas. We’re likely to work on keeping his upper body strength, increase his ability to leap higher , speed over 10 yards etc rather than add the proverbial yard of pace to his overall speed.