That's true but resale value still drops off dramatically past 30 years old. I didn't say he was on the decline due to age, I said he was on the decline because last couple of seasons he's averaged 1 in 4, before that he was just shy of 1 in 2 for a few years, and before that he was, what I'd term, "prolific". The stats indicate he's fallen off the wagon recently.
Yes he could rediscover his past form, but is that a gamble we want to be taking? If he doesn't, he will literally be worthless as noone will want a 31-year-old who's been in ****e form for 3 years. We would, yet again, be stuck paying inflated wages to a bench warmer while he winds his contract down. And it's (potentially) £15m down the swanny. Another Rodwell. That's the risk.
I'd rather we use that money on another striker we've been linked with - Bas Dost. He's a unit so gives us another option, has a better scoring record over recent years than Dzeko in a stronger league, and is only 27 so has resale value. A much better prospect all-round imo.