From around 6 months,maybe earlier my daughter has been putting things in her mouth.She was already taking purees so I just sat her in her highchair and gave her things to try,pieces of cheese,fruit,biscuit,cheerios.I was right there beside her I let her experiment while I did the dinner or other stuff in the kitchen.She wasn't going to choke with me right there.
Matilda's now 15 months,she's been feeding herself for 6 months.Once I realised how much she could chew with gums and a couple of teeth I stopped doing the purees and just gave her food cut up.
You have to let them try,and be prepared for mess.Feeding themself is a learning process.Matilda still eats her dinner with her hands mostly,which isn't pretty,but spoons and forks are next thing to learn,she's feeding herself well.It's certainly been easier than trying to introduce lumps to a fussy one year old