WTB: second hand hybrid/mountain bike to fit someone between 5'3" and 5'5" (160-166cm)

My younger brother has his birthday coming up and could do with a better/bigger bike. This is to be used in the countryside so a mixture of on and off road. He's not a particularly keen cyclist so this doesn't need to be flash but lighter than the Apollo I rode 12 years ago. I reckon some sort of hybrid would be good or a mountain bike that can have the suspension switched off for use on roads. He is 11 and is currently 160cm so anything that will fit him now but allow room for him to grow. Risers rather than drops if you've got a hybrid.

The budget is <£250. And my mum (who is 165cm) plans to use the bike when he outgrows it. She went to their LBS and was particularly taken by what I think might have been a Scott Contessa, amazed by how light it is compared to her 30 year-old Giant... duh.

Anyway, open to all sensible suggestions. Post/message me what you've got. The birthday is in a week so doesn't leave much time but I guess it's not the end of the world if it's a little bit late. In time for the summer holidays would be great. I'm in London, they're in Basingstoke. Willing to travel within reason to collect.

When my son started to ride to school at the age of 10 I bought him a small Specialized sirrus (back in the day when the base model got you Ritchey Cranks and Tiagra level components), guard and rack mounts and can take wider tyres for a bit of trail riding. 15 years later and he's on a Sirrus Expert with CF forks/stays/seatpost though doesn't ride as much.

You can also find the specialized globe in smaller versions as well as a lady versions, they often come up in neutral colours.
Other good hybrids from the likes of Marin (Larkspur, Lucas Valley etc), Trek (FX series) come up from time to time in smaller frames that are basically unisex bikes.

As I alluded to above, many of the newer bikes are nice and shiny but come with much lower spec components for same/higher prices compared to their counterparts from 10 years ago and not for the better IMHO.
luck hunting

Thanks for the recommendations. That's a good point about there often being higher spec components on older bikes - more reason to go down the second hand route (although I'd have thought that they might also tend to be a little more weighty than today's equivalents). I'll have a look at these models and advise the necessary parties on what I think would be best.

Thanks for your help