6 month old not rolling OR sitting

[Pickleypickles]

My dd is 6 months old and still does roll over or sit up, she can sit if you lean her on a cushion or something but not on her own for even a second and she doent roll either way, never has. I kept reading people with similar worries but they all seemed to say they did other things early like they could sit up and things. My dd cant even hold her own bottle, she is a very happy baby and i do lots of tummy time but it doesnt seem to be helping she can only lift her head and shoulders off the floor for about 30 seconds before she cant hold it any longer.
Should i be worried? Is this normal, is she just a bit slower?
TIA

6 months is still young to sit. Current NHS guidelines say 6-8 months, so she's right at the beginning.

One of mine didn't roll until 13 months, long after he could crawl! Some babies never roll.

It's also very early to expect her to hold her own bottle.