No, you aren't getting old they just make them heavier now a days. Just like some guy sneaks into my house every few months and steepens my staircase. 
It is the darn crap the seats are made of that causes problems. Old time outhouse seats made of wood are in demand today as a collectors item. Yes people do collect darn near anything today.
Got to figure these seats made of good wood have been sat on for generations of people and are still in good working fashion. The seats were not made for comfort for 15-30 minutes, they were for a quick use as we all know from camping there could be a spider or snake crawling up to bite you in the butt.
Peoples Court had a case where a neighbors pet snake got into the sewer system in an apartment building and arrived in a woman's toilet. ----After seeing that case I all ways turned on the light in the bathroom and checked before I sat down when living in Apartments.
Seats, those made of plastic wear better then the cushion kind that split open after a year or so on little traffic.
Porcelain are hard to find and attach to the plastic toilets made today. Interesting study of the seat you need to feel the most secure sitting on.
Good luck as sometimes the most basic needs are the hardest to find.
