Given the low market competition for Machado’s and Harper’s services, I seriously wonder how many teams would be interested in adding Trout. He’ll be looking for a contract that covers his age 29-35+ seasons.
Trout’s closest recent comparable is Pujols and his contract with the Angels through age 32-41 has been rough. Probably close to worst case scenario for Trout’s career trajectory, but still worth considering. Injuries and age can erode even world class talent very suddenly.
Who was the last hitter who had Hall of Fame production into his 30s with no suspected use of “performance enhancers”?
Other than the fact that they both put up MVP-caliber seasons every year of their career starting at their rookie seasons until Pujols' age 30 season, Trout and Pujols aren't truly comparable; Trout plays a more important defensive position and is a better athlete.
Trout is probably the closest historical match for Mickey Mantle. I don't really like the comparison because Mantle was a switch-hitter and had significantly more power. But most of Trout's seasons could be slid into Mantle's career and you wouldn't know the difference.
I think Trout at this point of his career is probably most similar to a 25-28-year-old "pre-roid" Bonds.
As to your question, it is perfectly normal for Hall of Fame-caliber players to be quite productive well into their 30s and even until age 40 or so. Not sure who you suspect of PED use but guys like Henderson, Murray, Winfield played into their 40s and were productive. Chipper Jones won a batting title at age 36 and was a good hitter at age 40. Mike Schmidt was Mike Schmidt until 37. Mays, Aaron, Williams had very long careers and were great just about until the end.