I turned 50 this past year and ride a 05 wr450f with a few mod's +pipe etc.
love the bike, it's more capable then me and I'm a little on the slow side, but I just make up for it by going farther. Rode my first race last month the Desert 100 in Odessa, Wa , did the 1 loop 50 miler and had a great time.
I maybe slowing down but I don't plan on getting off it anytime soon.
I'm 49 and still trying to adust to my 05 WR450. I bought it for the e-start, but I'm really missing my XR400 that I sold. The WR has a really hard seat and seems harsh when just trail biking...going slow. The bike behaves great when you get after it attacking whoops, etc. I have only 3 hrs saddle time, but before I spend any money on GUTS seat, bar risers...I want to make sure I'm keeping the bike.