There is also another POD - around 55 or sometime he did see a nutritionist/health expert who said that he could keep his diet as long as he kept up his exercise and made him go on 20 mile hikes, which basically had the effect of exhausting a 50-something year old man. If he had saw a different health expert, one with a little more backbone, who would have said that he can't keep his eating habit, his life could have been extended.
Some may say this would have been out of Teddy's character, but if he saw it as a challenge, something to overcome, a fight if you will, then yes I see him changing his eating habit. It probably only buys him a year or two, but also probably makes his later years healthier.
He also contracted blood poisoning while in South America when a boat gashed his leg when he was in a river. So no expedition down South America way helps that too.
All in all, I say with these two changes 1935 at the latest, especially if he wins the Presidency again in 1920, seeing how that has a way of aging a man.
Also, somehow he has to cut down on his speaking engagements while POTUS in 1920. In Colonel Roosevelt it was framed that those seemed to age him more than anything.