what does this mean

Dude you're reading too much into this. I am a girl and even though I decline someone's request to hang out, I will still like their message, it doesn't mean anything.

Just out of interest, why would you suddenly want to ask a girl to hang out after not speaking for over a year?

I mean if its me and one of my guy friends who I haven't talked to in over a year suddenly ask me to hang out, I will find it a bit strange and refuse as well cause I don't what he's been up to in that time and why he hasn't messaged me in all this time if we are good friends unless something is up.

she liked the message after a few days though, why would she do that if she previously said no and didnt want to hang out? and why would she then randomly like another message from years ago, which was nothing significant

Its just to be nice, that's all. Honestly, I do the same, even though its been days or weeks, I would still like the message.
But maybe the question should be why do you care so much about something so simple as her liking her message when she already declined to hang out. Do you have some feelings for her? Otherwise you wouldn't be reading so much into it.

yes i do have feelings for her, im still confused as to why she has randomly likedy messages, should i ask her why?

i asked this girl who i used to be friends with years ago if she wanted to hang out, i hadnt spoken to her in over a year, she says no thanks the next day but then about 9 days later she liked the message (this is on Instagram) then a few days later (yesterday) she liked my last mesaage to her from years ago, what does this mean

You're only 17. If you were friends 'years ago', how old were you both, 12? Leave it; people change and mature.

we were friends from 13 -15 basically