Now that we have got the results, I am more confident to reply to your post.
DS found St Olave's Stage 1 papers harder than Bexley (top 180) and Kent (141 for Maths). From what I gathered, the maths at SO would not go above the primary school curriculum (unlike some independent schools) but would require a higher degree of problem-solving. My DS is a maths geeks who is fascinated by numbers, patterns, and equations, so it sort of comes naturally for him. We only looked at SO because DS's friend was preparing for it, and DS was so impressed by the robotics on offer that he insisted he wanted to try.
We only started 'proper' 11+ preparation after Feb half-term in Y5, but prior to that, we had been making sure that he was confident with his core skills and played games like King of Maths to encourage him. His primary school teachers had been great at setting extra challenges for the higher achievers. I also introduced the concepts of algebra (finding the unknown) and led him to some maths puzzle books. Since Feb, we used a combination of CGP books (10-minute tests), Schofields' Mental Arithmetic (Book 5 and some of Book 6), GL practice tests, Bond papers, some independent schools' past papers, and an online revision course (not great value for money imo but DS loved gaining points; also his aunt part-funded it). We sent him to SO's mock test back in May, and some local mock tests for Bexley over the summer just to check on progress. We kind of guided him in terms of timing, exam techniques, and a few tricks, but he has done most of the preparation himself. For us, the problem was stress and emotion management rather than the actual content. Initially, I thought he had to get over 90% in raw score (got scared after reading forum posts), and unwittingly told him so. He became so upset whenever he got a question wrong. He broke into tears on parents' evening in front of his teachers because he didn't get top mark at one of his maths topics. It has taken us some time to rebuild his confidence, and that's why since then I had largely let him explore the materials on his own, only offering help when he genuinely needed it. I am so proud of him whatever happens to stage 2.
In summary, the 11+ preparation depends on the child. I would suggest you first download the sample questions (both stage 1 and 2) from the school's website to get an idea of the questions asked (and the topics). I hope my experience helps not just in terms of the content but the emotional challenge of the whole 11+ process.