My little boy is four months old now and I know that awake windows are just a guide so they aren't up for a stupidly long amount of time etc. I go off of his cues and at the moment he can only manage being up an hour in the morning and then one hour and 15 or 20 minutes throughout the day. I thought awake windows were supposed to lengthen as they get older? Any advice?
Yes they are going to lengthen as he gets older. Awake windows are due to sleep pressure and essentially the amount of adenosine (which is a hormone) that your baby can accommodate at one time. Some babies can accommodate more, some less.
But over the next few weeks it would not harm to gently see if you can lengthen his awake windows by maybe 10-15 minutes to help him gradually get used to being awake for longer.
It's normal - some of them sleep more, others less (mine sleeps less)! But it will get better, don't worry!