Do you think the likes of Luca Toni and Fabio Quagliarella would be scoring goals at the same rate in the Premier League? Genuine question. There's a reason that in Italy players are able to play in to their mid 30's no hassle and a lot of them 'peak' at that level, it's not because they're fitter than their counterparts from other leagues, it's because the league is slower paced and therefore they can play on for longer. I watched Luca Toni play when he was scoring, he ran like he was going through cement. Luca Toni would not have gone to the PL in his mid 30's and scored a lot of goals.
Zlatan was one of the most talented players of his generation so was able to do well in the PL, but he still suffered a massive drop from his Ligue 1 form and suffered a lot due to a lack of pace. His technical ability allowed him to score a good amount of goals, but IIRC he had a pretty poor conversion rate and was often at fault for slowing down play. Zlatan did not tear up the Premier League. The better question is how many strikers in their mid 30's are still able to compete for top scorer in the Prem? It doesn't really happen. Even the greats like Van Persie, Drogba, Rooney etc slowed down massively in their early 30's, there are far more examples of older players thriving in Italy. It's less demanding on their bodies because it's less physical, slower, you play less games and get a break. That's not coming from sky sports stereotypes, that's coming from me watching Serie A plenty in the last few years (haven't had much of a chance this season, but I used to do a lot of betting so watched games from pretty much all the major leagues).
Stereotypes play their part and it's not as exaggerated as Serie A being a haven for old fogies, but I wouldn't say that there's no basis to the idea that older strikers (or players in general) can be more at home in Serie A. I'm going to go ahead and guess you watch both Serie A and PL games, would you not say on average that premier league matches are more intense and played at a faster pace? Again, it's not necessarily that I think the Premier League is superior and harder to play in, just that I think it favours different skillsets to Serie A. Off the top of my head I can think of Lichsteiner coming in this season and being dreadful, or Patrice Evra going off and being pretty successful for Juventus despite looking done in England. I'm sure there's more, though I don't think in general that Italy would be a preferred move for most PL players.