Notacop is right your old oil will stink and a change will help.
Now the problem is oils aren't oils, a 10w in one brand will be different to a 10w in another brand so you have some reading ahead of you.
I used (ATF) automatic transmission fluid in my 09 Wee and I was happy with the results.
All my farm bikes also get ATF, it lasts longer than fork oil and seems to stay behind the seals better, EG: less leaks past old seals.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.