Miller remains a key man for Mark Warburton's Glasgow Rangers side and recently brought up a landmark goal for the Ibrox club.
Rangers' Kenny Miller
The 36-year-old - who turns 37 in December - continues to be a key part of Mark Warburton's plans at Ibrox, and brought up a landmark goal in his most recent appearance.
The winner against Inverness was the 100th goal of his Gers career. And with the strike making him the side's current top goalscorer in the Scottish Premiership, Johnston has tipped the former Scotland international to continue to be an important member of the squad for a while yet.
"If he watches himself, he has not got a weight problem, I don't think he smokes or drinks. He has looked after himself so he can play for another couple of seasons yet," he said, as reported by the Evening Times.
"It is brilliant to have someone like Kenny in the dressing room. He has been a great professional all through his career and I think the lads there will look up to him because of what he has done in his career.
"He can play for another couple of seasons no problem and there are plenty of goals left in him yet I am sure."
While Warburton may perhaps prefer a younger player to be contributing the goals, there is no doubt that he will be delighted with Miller's form since the club's return to the top flight.
Rangers manager Mark Warburton
The Light Blues have seemingly found things more difficult than they were anticipating following their promotion, but the former Wolves man has made the transition and integration of several new signings much easier as he continues to score important goals.
All three of his strikes this term have proved to be winners, so Rangers would have surely been even further off the pace had they been without him.