I grew a few pears from seed after taking some from my kids left over food.

I took my two strongest seedlings and have been growing them together.

I'm hoping that over the years they will fuse and i can make a twin trunk pear bonsai

I recently taped the trunks to keep them close together.
I've never done a fusion before so any tips on success would be appreciated.
I'm not sure if i sand down the sides of the trunk a little bit in a few years and tape it up will work better than just leaving them next to each other.
either way its a fun experiment.

The best way to get trunks to fuse is wire and very tight, and as low down as possible. You could also use cable ties.

perfect, my next question is, is there an age thats too young to start or the sooner the better, or does the tree need strength first?

No, the younger the better almost. It will take two or three years to fuse, possibly a bit longer. I have done some clumps of Field Maple and will leave the wire for at least three years, but just treat them as a normal tree.