It can be harder to make friends as you get older. People are busy, they already have 'enough' friends bearing in mind what spare time and mental energy they have, they worry what demands a new friendship will place on them, they don't want to get friendly and then let someone down because they don't have the time. That last one I've done myself - got on with someone great, thought 'we could be friends' then realised that on top of work / family / doing a house up / existing interests, and the fact I only see my best, old friends 4 times a year tops, how would I fit this new person into my life? Would I be setting myself up to let them down? Would they expect to talk weekly and see me monthly, because I wouldn't have time for that. So I back off. Perfectly lovely people.
So at least in part you're battling against things that are outside of your control. It's harder to make friends as an adult.
As for your old friends - you have to decide... are you happy to keep being the one making suggestions to meet up, knowing you like them and enjoy their company when you see them? Some people are organisers, some rely on others to organise. I have a lovely old friend (who I see twice a year tops) who is great company, has been brilliant if called on in a crisis, but is rubbish at keeping in touch generally. If I ask her to meet for a coffee, she'll be there and will be her lovely self. She admits that, with life and work and children and ill parents etc, she just doesn't think to suggest meeting friends.
If you feel it's more than that, and that they are avoiding you personally, then it looks like those friendships have run their course. It happens. Don't give up on making new ones, it just takes more effort now. I actually prefer to not focus on 'new friends' but to do things that make me happy (hobbies and interests) and to be friendly with the people there, whilst not expecting to make individual friendships. It's less pressure, and you have the hobby in common before you even start.