This isn’t medical advice but it sounds to me like you'd be fine. I always recommend hiring a porter regardless of age; it's a huge help to have someone carry your stuff and leave your hands free for taking photos.
If you think you need some extra support you can hire a group to carry you on a rather unglamorously-named "stretcher" (it's better than it sounds!) You generally pay $10-$15 per person for the porter, and you might consider adding a tip of a similar amount. The "stretchers" cost around $100. These services are community-run initiatives and are a big boost to a family's income. All this can be arranged on the morning of your trek, during your briefing.
Also consider the location of your lodge and the gorilla family that you're assigned to track. Don't be shy in stating your tracking preferences during the morning briefing. The rangers want everyone to have a good – and safe – time so they will do their best to make sure that people with similar fitness levels are grouped together and assigned to track a more accessible gorilla family.
The Habinyanja family in Buhoma (Uganda) is well-known for being quite close to a number of the lodges. I tracked this same family a few years ago and had a lovely hour in search of them, before spending an hour with them. It took a little less than an hour to get back to the lodge, so about a three-hour round trip. Your tour operator should be able to identify a gorilla family and lodge combination that suits your fitness and ability levels.
Good preparation is also important. Local people love wearing gumboots (they keep out the ants as well as the mud) but walking boots with ankle support are the best option I'd say. I'd suggest bringing walking pole(s) or a stick. Sticks can also be bought or borrowed from your lodge.
