I am very new to singing, even though I am 68 ;-) 

I am having trouble finding 'where' I should sing. Sometimes I start of in a low vocal range, sometimes in a higher range. Often I switch between the two in the same song. 

Any ideas on how to stop this, or is it just practice and extending my range? I would love to just start in the right range and do the whole song in without keep switching from chest to head voice.

Great question, Tony! Sounds like you're not sure which octave to sing in, which will improve with time & experience matching pitch and confirming you're in the correct octave with a chromatic tuner. I recommend the following lesson series for instruction and exercises to help you with that skill! 

https://www.30daysinger.com/tutorial/how-to-sing-in-tune-for-beginners-part-1

https://www.30daysinger.com/tutorial/how-to-sing-in-tune-for-beginners-part-2