Hmmm. Didn't you say that YOU initiate the topic of weather but you think it's the old people who are obsessed? At this very moment you know, there may well be a discussion at Letsnotdiejustyet.com where people are discussing you and your fixation with weather.
Seriously, weather is a "safe" topic in situations where people who have little in common or at least don't know if they do think a little more interaction than a "hello" is appropriate. I always have "weather" chats with our mailman. He always initiates them and he's younger than I am. Neither of us knows much about the other and I doubt either of us want a conversation that will degenerate into an argument so "Man, this cold weather really sucks" is much safer than "How about that same sex marriage law?"
It is true that weather becomes more of an issue for you as you get older. When those massive heat waves hit the midwest and kill a few people it's nearly always older people who die. An ice storm is much less a problem for an 18 year old who has better balance than an 80 year old and who is much, much, less likely to die from falling on that ice. Old people who are on fixed incomes can take a real financial hit if there's prolonged stretch of very cold weather and they use more gas, oil, or electricity heating their homes than they'd budgeted for.
But if you'd rather not talk with someone about the weather then don't bring it up.