How to get old grout white again.

you can get colored grout sealers, i believe it does come in white as well as other colors. get a kneel pad if its a large area to do, and get the same lot no. if multiple vials are required.

Well then why not paint it the same colour as tiles?

Baking soda and white vinegar

I used a commercial grout cleaner that I got from Home Depot or Lowes. My kitchen grout (which used to be a light beige) was nearly black because I neglected to seal it when it was new. The cleaner brought it back to original; I was amazed.

Make a paste of bleach and baking soda. Use a toothbrush to clean the Great with the paste. Leave the residue on for an hour. Rinse. If you see improvement, repeat. If you don’t. Paint with a waterproof latex or white silicone. Best wishes ☺️

Sometimes stains will not come out no matter what you use or how hard you scrub. I had to paint grout lines and floor looks like new. Would recommend highly. Great results. Just paint the lines with a small 1" brush; wipe off excess from tiles. Let dry and you're go to go. It is still great looking after 3 years!

Looks like this is what I will end up doing. Thanks